UC-NRLF 


33    3Mfl 


MECHANICAL 
DRAWING 


PHILLIPS  AND  ORTH 


EDITOR 
FRED   D.   CRAWSITAW,   B.S.,   M.E. 

THK   UNIVERSITY  OF  AVISCONSIN 


MECHANICAL  DRAWING 

FOR 

COLLEGES  AND  UNIVERSITIES 


BY 

JAMES  D.  PHILLIPS,  B.S. 

PROFESSOR  OF  DRAWING  AND  ASST,    DEAN,  COLLEGE  OF  ENGINEERING 
THE  UNIVERSITY  OF  WISCONSIN 

AND 

HERBERT  D.  ORTH,  B.S. 

INSTRUCTOR  IN   DRAWING,  THE  UNIVERSITY  OF   WISCONSIN 


SCOTT,  FORESMAN  AND  COMPANY 

CHICAGO  NEW  YORK 


COPYRIGHT  1915 

BY 
SCOTT,  FORESMAN  AND  COMPANY 


PUBLISHERS'  NOTE 


The  present  volume  is  for  use  in  University 
classes  and  is  complete  in  itself.  It  is  to  be  fol- 
lowed, however,  by  a  book  for  high  schools  by 
Professors  Crawshaw  and  Phillips;  and  the  two 
books  will  form  a  complete  course  in  Mechanical 
Drawing  for  High  School  and  University  work. 
In  this  connection  the  publishers  wish  to  an- 
nounce their  Vocational  Series  for  Schools  and 
Colleges  under  the  editorial  supervision  of 
Professor  F.  D.  Crawshaw  of  the  University  of 
Wisconsin.  This  series  is  intended  to  supply  an 
increasing  demand  for  textbooks  for  use  in  the 
vocational  courses  that  are  now  being  so  widely 
adopted  as  a  part  of  public  education. 


331009 


PREFACE 

A  drawing  is  a  plan,  and  sometimes  also  a  specification,  for 
construction  work  or  the  assembly  of  constructed  parts.  From 
the  beginning  of  time  drawing  has  been  a  means  of  expression 
and  consequently  is  a  form  of  language.  Only  within  recent 
years,  however,  has  the  art  of  graphical  expression  been  an  im- 
portant element  in  the  process  of  developing  machinery  and 
structural  work.  Today  a  drawing  is  one  of  the  first  steps  in 
the  production  of  practically  all  machines  and  structures. 
Mechanical  drawing  is  the  particular  form  of  drawing  used  for 
this  purpose.  The  commercial  value  of  mechanical  drawing  is 
therefore  quite  evident. 

Drawing  has  educational  as  well  as  commercial  value  if  it 
is  properly  taught.  It  is  recognized  as  one  of  the  best  known 
means  of  training  for  habits  of  observation  and  perception.  As 
a  means  of  strengthening  the  imagination  and  developing 
coordination  between  the  hand  and  eye,  it  has  few,  if  any,  equals. 

It  has  been  the  aim  of  the  authors  to  arrange  a  course  in 
drawing  which  will  develop  these  powers,  and  which  at  the  same 
time  will  give  the  student  an  appreciation  of  the  best  commercial 
drafting  room  practice  while  making  complete,  accurate,  and 
well-finished  drawings  of  industrial  projects.  The  course  pre- 
sented in  this  book  is  designed  for  college  students  who  have  not 
had,  necessarily,  previous  experience  in  drawing.  Both  the  plan 
and  the  details  of  the  course  have  been  carefully  worked  out  and 
repeatedly  tested  under  practical  conditions.  The  present  form 
and  content  of  the  course  represent  the  result  of  years  of  ex- 
perience in  teaching  drawing.  The  course  has  fulfilled  the  edu- 
cational and  commercial  requirements  as  set  forth  herein. 

As  an  example,  each  element  in  drawing  is  treated  separately 
before  the  elements  are  combined.  By  concentration  of  thought 
and  effort  and  by  means  of  repeated  performance  of  similar 

7 


8  MECHANICAL  DRAWING 

operations,  the  student  is  enabled  to  comprehend  the  theory 
involved  and  to  develop  technique  and  skill  in  a  minimum  of  time. 

The  elements  or  general  divisions  in  drawing  are  introduced 
in  the  order  in  which  they  would  naturally  occur  in  a  commer- 
cial drafting  room,  as  follows:  Perspective  Sketching,  Ortho- 
graphic Sketching,  Pencil  Mechanical  Drawing,  Tracing  and  Blue- 
printing. "Within  these  divisions  the  ideas  of  progression  and 
concentration  are  again  carried  out  by  introducing  lines  and 
conventions  in  the  following  progressive  order:  Straight  Ver- 
tical and  Horizontal  Lines,  Straight  Oblique  Lines,  Large  Cir- 
cles and  Arcs  of  Circles,  Small  Circles  and  Arcs  of  Circles 
Tangent  to  Straight  Lines,  Arcs  of  Circles  Tangent  to  One 
Another,  Irregular  Curves.  It  will  be  noticed  that  the  drawing 
of  tangencies  is  deferred  until  the  end  of  Chapter  IV.  This  is 
done  to  prepare  the  student  for  the  necessary  conventions  used 
in  section  views  and  to  give  him  considerable  skill  in  the  handling 
of  instruments  in  all  fundamental  operations. 

Special  attention  is  called  to  the  subject  of  Perspective 
Sketching,  as  treated  in  Chapter  I.  The  authors  have  endeav- 
ored to  reduce  this  subject  to  its  lowest  terms  for  use  in  me- 
chanical drawing  where  it  serves  principally  to  interpret  ortho- 
graphic drawing.  In  commercial  practice  the  representation 
of  objects  by  perspective  is  increasing  and  hence  it  would  seem 
that  every  student  of  mechanical  drawing  should  become  fa- 
miliar with  at  least  a  simple  treatment  of  45°  perspective,  the 
form  emphasized  in  this  text.  It  is  assumed  that  the  time  de- 
voted to  this  part  of  the  course  will  not  exceed  one-fifth  the 
total  time  for  the  work  of  the  first  four  chapters — approxi- 
mately one  hundred  hours. 

Every  problem  given  in  this  course  requires  thought  on 
the  part  of  the  student  to  reach  a  solution.  The  various  methods 
of  presenting  problems  and  the  solutions  required  are  exemplified 
in  Plates  2,  7,  13,  18,  26,  29,  32,  and  35.  The  problems  of  the 
course  have  been  carefully  chosen  to  illustrate  principles  of 
representation,  dimensioning,  etc.,  and  are  arranged  in  accord- 
ance with  the  principle  that  the  more  advanced  the  position  of 
the  problem  in  the  course,  the  more  difficult  its  solution  from  the 
standpoint  of  both  the  theory  and  the  technique.  Groups  of 


PREFACE  9 

problems  are  presented  for  most  of  the  plates,  from  which  prob- 
lems may  be  assigned,  thus  affording  a  means  of  suiting  the 
problem  to  the  ability  of  the  student  and  of  lessening  the  ten- 
dency of  students  to  copy  from  others. 

With  each  orthographic  problem  a  type  problem  is  given. 
This  type  problem  consists  of  the  given  data  and  the  solution  of 
a  problem  similar  to  that  assigned  to  the  student.  Example : 
Figs.  65,  68,  and  69  show  the  given  views,  constructive  stage  of 
pencil  mechanical  drawing,  and  the  completed  drawing.  By  this 
method  suggestions  are  given  as  to  methods  of  representation 
and  dimensioning,  while,  at  the  same  time,  a  high  standard  of 
technique  is  set  for  the  student. 

It  has  been  the  aim  in  arranging  the  material  and  selecting 
the  problems  of  the  course,  to  distribute  the  introduction  of 
theory  and  the  use  of  the  various  instruments  in  such  a  way  that 
the  student  will  comprehend  both  the  theory  and  its  application. 
The  means  used  to  this  end  is  A  COURSE  IN  WORKING  DRAWINGS, 
supplemented  by  lectures  and  demonstrations.  By  applying 
theory  in  a  well  graded,  practical  problem,  immediately  after  the 
theory  is  presented  the  student  should  develop  a  full  compre- 
hension of  drawing  as  it  is  used  in  commercial  practice. 

To  aid  the  instructor  in  securing  the  viewpoint  of  the  au- 
thors in  the  teaching  of  the  course,  Chapter  X,  The  Instructor's 
Guide,  was  prepared.  It  attempts  only  to  emphasize  the  prin- 
cipal points  which  the  authors  have  found  important.  It  should 
reinforce  rather  than  limit  the  instructor's  individual  method. 

The  authors  wish  to  express  their  appreciation  of  the 
cooperation  of  Professor  Crawshaw  from  the  very  beginning 
to  the  end  of  the  book.  He  has  been  a  co-author  in  its  production. 

THE  AUTHORS. 


TABLE  OF  CONTENTS 

CHAPTER  I 

PAGE 

PERSPECTIVE   SKETCHING 13 

CHAPTER  II 

ORTHOGRAPHIC  SKETCHING 50 

CHAPTER  III 

PENCIL  MECHANICAL  DRAWING 77 

CHAPTER  IV 

TRACING  AND  BLUEPRINTING 104 

CHAPTER  V 
INSTRUMENTS  AND  MATERIALS 126 

CHAPTER  VI 

CONVENTIONS 145 

CHAPTER  VII 
LETTERING 176 

CHAPTER  VIII 
ADVANCED   DRAWING 225 

CHAPTER  IX 

AUXILIARY    VIEWS,     ISOMETRIC    AND     CABINET    DRAWING, 

TABLES,  ETC 255 

CHAPTER  X 
INSTRUCTOR'S   GUIDE 266 

OUTLINE  OF  COURSE  IN  MECHANICAL  DRAWING 274 

11 


CHAPTER  I 

PERSPECTIVE  SKETCHING 

GENERAL  PRINCIPLES 

A  freehand  drawing  in  outline,  which  represents  an  object 
as  it  appears  when  viewed  from  any  given  position,  is  called 
a  perspective  sketch. 

Fig.  1  is  a  perspective  drawing  of  a  try-square.  In  this  case 
the  try-square  is  placed  with  the  blade  and  beam  making  equal 
angles  with  the  horizontal  line  marked  horizon.  The  try-square 
is  shown  as  an  observer  would  see  it  when  standing  directly  in 
front  of  A  B,  with  his  eye  on  the  same  level  as  S. 

In  Fig.  1  the  line  marked  horizon  represents  a  line  in  space 
at  an  infinite  distance  in  front  of  the  observer.  The  eye  of 
the  observer  is  on  a  level  with  this  line  and  is,  consequently, 
above  the  level  of  the  try-square,  which  rests  on  a  horizontal 
plane. 

The  horizon  or  horizon  line  is  therefore  an  imaginary  hori- 
zontal line  on  a  level  with  the  eye  of  the  observer  and  at  an 
infinite  distance  in  front  of  him.  The  apparent  meeting  of  sky 
and  water  when  one  looks  over  a  large  body  of  water  is  an 
example  of  an  horizon. 

Since  the  horizon  is  always  on  a  level  with  the  eye  of  the 
observer,  it  follows  that,  as  the  eye  is  raised  or  lowered  to  secure 
a  different  view  of  the  object,  the  horizon  will  be  raised  or 
lowered  the  same  distance. 

Direction  of  Lines  in  Perspective.  Referring  again  to  Fig.  1, 
we  note  that : 

1.  The  vertical  edges  of  the  try-square  are  represented  by 
vertical  lines  in  perspective.  Example  :  A  B  and  C  D. 

13 


14 


MECHANICAL  DRAWING 


2.  The  horizontal  edges  of  the  try-square  receding  to  the 
right  and  left  converge  to  points  on  the  horizon  to  the  right 
and  left  of  the  observer.  These  points  are  called  vanishing 
points.  Since  the  beam  and  blade  of  the  try -square  make  equal 
angles  with  the  horizon,  the  vanishing  points  are  at  equal  dis- 
tances to  the  right  and  left  of  the  point  S,  which  is  vertically 
above  A  and  directly  in  front  of  the  observer. 

A  vanishing  point  is  the  common  intersection  of  two  or  more 
converging  lines  which  represent  parallel  receding  edges  of  an 
object. 

All  parallel  horizontal  receding  lines  must  converge  to  the 
same  point  on  the  horizon.  Example:  The  horizontal  lines  of 


FIG.  1.     PERSPECTIVE  OF  TRY-SQUARE 


the  try-square  converging  to  the  right  in  its  perspective  meet 
in  VR.  Likewise  all  the  horizontal  lines  converging  to  the  left- 
meet  in  VL. 

Measurements  in  Perspective.  Equal  distances  on  the  front 
vertical  edge  of  an  object  are  represented  by  equal  lengths 
in  perspective.  Example :  In  Fig.  1  the  blade  of  the  try- 
square  divides  the  front  vertical  edge  of  the  beam  of  the  try- 
square  into  two  equal  parts  which  are  shown  by  lines  of  equal 
length. 

Foreshortening  is  the  process  of  shortening  parts  of  a  per- 
spective of  an  object  so  as  to  give  the  impression  of  true  form 
and  proportion. 

Since  the  parallel  receding  lines  in  perspective  converge, 
equal  vertical  distances  included  between  two  such  lines  will  be 


PERSPECTIVE  SKETCHING  15 

shorter  as  their  distance  from  the  observer  increases.  Example : 
The  edges  A  B  and  C  D  of  the  try-square  are  equal  while  in 
the  perspective  of  the  try-square,  C  D  is  shorter  than  A  B. 
Fig.  1. 

On  horizontal  receding  edges  equal  distances  are,  also,  rep- 
resented by  shorter  lengths  as  the  distance  from  the  observer 
increases.  Example :  In  Fig.  1  the  spaces  between  the  lines 
representing  the  one-inch  marks  grow  shorter  as  they  are  farther 
away  from  the  observer. 

The  Cube  in  Perspective.  Thus  far  only  a  general  consid- 
eration of  perspective  has  been  given.  The  following  is  an 
application  of  the  principles  thus  far  developed  to  the  repre- 
sentation of  a  one-inch  cube. 

In  this  course  the  cube  will  be  regarded  as  the  basic  form 
for  all  perspective  drawing.  In  Fig.  2  the  eye  of  the  observer 
is  directly  in  front  of  the  point  S.  The  vertical  faces  of  the 
cube  make  45°  with  the  horizon  and,  also,  with  the  direction 
in  which  the  observer  is  looking.  This  is  sometimes  referred  to 
as  45°  perspective,  and  is  the  kind  emphasized  in  this  course. 
In  45°  perspective  the  distance  from  the  point  directly  above 
A  (S  in  Fig.  2)  to  the  vanishing  points  and  to  the  eye  must  be 
equal.  In  this  course  14"  is  used. 

The  edges  of  the  cube  are  one  inch  long.  Therefore  the 
front  vertical  edge  of  the  cube  is  drawn  in  its  true  length. 

The  principles  already  developed  will  be  recognized  in  the 
following  analysis  of  the  perspective  of  the  cube. 

Since  the  side  faces  are  equally  inclined  to  the  direction  in 
which  the  observer  is  looking: 

1.  Angle  D  A  E  =  Angle  D'  A  E'. 

2.  Angle  F  B  11  =  Angle  F'  B  II'. 

These  angles  will  hereafter  be  referred  to  as  the  angles  of 
inclination. 

3.  The  perspective  of  the  corner  G  is  directly  above  A. 


16  MECHANICAL  DRAWING 

Due  to  the  convergence  of  A  D  with  B  F  and  A  D'  with  B  F' : 

1.  Angles  F  B  H  and  F'  B  H'  are  greater  than  angles 

D  A  E  and  D'  A  E'. 

2.  Lines  D  F  and  D  F'  are  shorter  than  A  B.     D  F  = 

D'  F'. 


TOVR 


TOVL 


TOVR 


TOVL 


FIG.  2.     PERSPECTIVE  OF  A  ONE-INCH  CUBE 

Due  to  the  convergence  of  A  D  with  D'  G  and  A  D'  with 
D  G: 

1.  G  D  and  G  D'  are  shorter  than  A  D  and  A  D', 

2.  G  C  is  shorter  than  C  A. 

Due  to  foreshortening: 

1.  A  D  and  A  D'  are  shorter  than  A  B. 


PERSPECTIVE  SKETCHING 


17 


RECTANGULAR  OBJECTS 
PREPARATORY    INSTRUCTIONS    FOR   PLATE    1 

The  following  is  a  list  of  the  materials  needed  to  make  the 
perspective  sketches.  Chapter  V  gives  a  description  of  each. 

1.  Drawing  board. 

2.  High    grade    drawing   paper   similar   to    Universal — 

9"  x  12"  sheets. 

f  *3TT 

3.  High  grade  pencils 

4.  Pencil  pointer. 

5.  Erasers — Ruby  and  Flexible  gray. 

6.  Thumb  tacks. 

In  preparing  to  make  a  freehand  perspective  sketch  the  steps 
should  be  taken  in  the  order  given  below : 

The  drawing  board  should  be  placed  on  the  desk  with  the 
longer  edges  parallel  to  the  front  edge  of  the  drawing  table. 
It  may  be  tilted  to  any  convenient  angle. 


BORDER  LINE 


FIG.  3.     POSITION  OF  THE  SHEET  ON  THE  DRAWING  BOARD 

A  sheet  of  paper  may  now  be  tacked  near  the  upper  left 
hand  corner  of  the  board  with  the  longer  edges  parallel  to  the 
longer  edges  of  the  board.  Fig.  3.  To  fasten  the  sheet  insert 


18 


MECHANICAL  DRAWING 


a  tack  in  the  upper  left  hand  corner;  square  the  paper  with 
the  board  and,  stretching  it  diagonally,  insert  a  tack  in  the 
lower  right  hand  corner.  Insert  a  tack  in  the  upper  right  hand 
corner.  Stretch  the  sheet  in  the  direction  of  the  lower  left  hand 
corner  and  insert  a  fourth  tack. 


FIG.  4.     SHARPENING  THE  PENCIL.     WHITTLING  AWAY  THE   WOOD 

To  sharpen  the  pencil  grasp  it  in  the  left  hand  as  illustrated 
in  Fig.  4  and,  with  the  knife  in  the  right  hand,  cut  the  shavings 
by  drawing  the  knife  toward  the  body  and  through  the  wood 


FIG.  5.    SHARPENING  THE  PENCIL.    POINTING  THE  LEAD 

only.  About  one-quarter  inch  of  lead  should  be  exposed  and 
the  wood  tapered  back  about  one  inch  from  the  lead.  Sharpen 
the  lead  on  the  surface  of  a  piece  of  sand  paper  or  a  file,  rotating 
the  pencil  so  as  to  produce  a  conical  point.  Fig.  5.  The  sharp- 
ened lead  should  be  slightly  rounded  on  the  end  in  order  that 


PERSPECTIVE  SKETCHING 


19 


soft  lines  as  shown  in   Fig.  6  may  be  produced.     This  figure 
also  shows  the  sketching  pencils  properly  -sharpened. 

The  Position  of  the  Hand  and  Pencil  in  Sketching.  In 
drawing  a  line  the  pencil  is  held  firmly,  but  not  rigidly,  between 
the  first  two  fingers  and  the  thumb,  as  in  writing. 


FINISHING    LINE 


4 

INCH 


MEDIUM     PENCIL 


CONSTRUCTION     LINE 

HARD    PENCIL 

FIG.  6.    SKETCHING  PENCILS  PROPERLY  SHARPENED 

In  sketching  a  horizontal  line  the  ends  of  the  third  and 
fourth  fingers  should  rest  upon  the  board  to  help  support  and 
steady  the  hand.  Fig.  7.  With  the  forearm  resting  on  the 
drawing  board,  the  hand  should  be  moved  from  left  to  right. 


FIG.  7.     SKETCHING  A  HORIZONTAL  LINE 


hinging  at  the  wrist.  This  will  permit  only  short  strokes,  about 
one  inch  long,  to  be  taken.  To  sketch  a  long  line,  therefore, 
one  must  join  together  a  series  of  one-inch  lines.  The  position 
for  each  stroke  should  be  obtained  by  moving  the  hand  and 
forearm  in  the  direction  of  the  line.  Each  section  should  be 


20 


MECHANICAL  DRAWING 


joined  to  the  preceding  one,  but  not  lapped  upon  it,  as  the 
lapping  of  sections  produces  an  undesirable  sketchy  effect. 

In  sketching  a  vertical  line  the  hand  is  placed  in  the  posi- 
tion shown  in  Fig.  8.  The  hand  rests  upon  its  side  instead  of 
upon  the  ends  of  the  third  and  fourth  fingers,  as  in  Fig.  7. 
The  pencil  is  moved  downward.  The  strokes  are  made  with  a 
finger  movement  while  the  hand  remains  stationary.  Each 
stroke  should  be  about  one  inch  long  and  succeeding  strokes 
should  be  joined  as  previously  described  for  horizontal  lines. 


FIG.  8.     SKETCHING  A  VERTICAL  LINE 


Do  not  allow  the  forearm  to  assume  a  considerable  angle  with 
the  vertical. 

The  Border  Rectangle.  Before  starting  a  sketch  draw  a 
freehand  border  line  one-half  inch  from  each  edge  of  the 
sheet. 

The  Constructive  Stage.  In  making  a  freehand  sketch  first 
draw  all  lines  very  lightly  with  the  5H  pencil.  The  general 
direction  of  a  long  line  can  be  determined  by  first  running  the 
hand  freely  from  one  end  to  the  other.  In  doing  this  the  pencil 
should  not  touch  the  paper.  The  line  may  then  be  drawn  in 
sections  as  described  above.  To  test  the  straightness  of  a  line 
place  the  edge  of  the  drawing  pencil  near  it.  The  outline 


PERSPECTIVE  SKETCHING 


21 


thus  secured  is  known  as  the  constructive  stage,  Fig.  9. 

The  Finishing  Stage.     When  the  constructive  stage  of  the 
sketch  has  been  completed  all  lines  except  those  forming  the 


FIG.  9.     CONSTRUCTIVE  STAGE 

outline  of  the  object  should  be  erased.  The  3H  pencil  should 
then  be  properly  sharpened  and  the  lines  of  the  object  traced 
over  to  make  them  true  and  uniform  in  width  and  grayness  of 
tone.  Fig.  10. 


FIG.  10.    FINISHING  STAGE 


*DATA  FOR  PLATE  1 

Given:     The  perspective  of  a  cube.    Fig.  11. 
Required:     To  copy  the  drawing  shown  in  Fig.  11  to  an 
enlarged  scale,  omitting  the  reference  letters. 

e  followed  by  the  letterin£  P^te  of  the  same 


22  MECHANICAL  DRAWING 

Instructions: 

1.  Draw  the  border  rectangle. 

2.  To  locate  the  perspective  of  a  cube : 

a.  Draw  two  very  light  horizontal  lines  X  VR  and 
Y  Z,  dividing  the  space  between  upper  and 
lower  border  lines  into  three  equal  parts. 


FIG.  11.     PERSPECTIVE  OF  A  CUBE — PLATE  1 

b.  Draw  a  vertical  line  V  "W  through  the  center  of 

the  sheet  and  S  U  midway  between  V  W  and 
the  left  border  line. 

c.  From  B  estimate  one  inch  up  on  S  U,  thus  locating 

A,  the  upper  front  corner  of  the  cube. 

3.  VR  is  about  J"  from  the  right  border  line. 

4.  Sketch  lightly  a  horizontal  line  through  A  and  con- 

nect A  with  VR. 


PERSPECTIVE  SKETCHING 


23 


5.  Get  the  direction  of  A  D'  by  drawing  the  angle  of 
inclination  D'  A  E'  equal  to  angle  DAE.  More 
than  one  trial  may  be  necessary  to  make  these  angles 
equal  as  illustrated  by  A  D'  and  A  D'".  Fig.  12. 


FIG.  12.     SKETCHING  THE  ANGLES  OP  INCLINATION 

Erase  each  trial  line  before  drawing  another,  until 
the  angle  is  correct.  Draw  lines  B  VR  and  B  F' 
in  the  same  manner. 

6.  To  obtain  the  width  of  a  vertical  face  of  the  cube  draw 
D  F  so  that  the  figure  A  D  F  B  appears  as  a  square. 


FIG.  13.    DETERMINING  THE  WIDTH  OF  THE  FACE  OF  THE  CUBE 

Fig.  13  shows  the  process  of  getting  D  F  located  by 
trial.  Erase  each  trial  line  before  drawing  the  next 
one.  Lines  representing  vertical  edges  may  be  tested 
for  direction  by  placing  a  pencil  along  the  line. 


24  MECHANICAL  DRAWING 

7.  Draw  D'  F',  making  A  E'  =  A  E.    Complete  the  per- 

spective of  the  cube  by  drawing  D'  VR  and  D  G. 
Fig.  11. 

This  completes  the  constructive  stage. 

8.  After  erasing  unnecessary  lines  the  outline  of  the  cube 

should  be  traced  over  with  a  well  sharpened  pencil 
to  produce  a  line  of  even  weight  and  uniform  shade. 
Fig.  10  shows  the  cube,  actual  size,  as  it  should 
appear  o-n  the  student's  drawing. 

9.  Write  the  plate  number  and  name  in  the  lower  right 

hand  corner  of  the  sheet  as  in  Fig.  11.  Remove  the 
sheet  from  the  board,  turn  it  over,  and  press  the 
paper  back  into  the  thumb  tack  holes. 

PREPARATORY    INSTRUCTIONS    FOR    PLATE    2 

A  Scale  of  Levels.  The  size  of  the  figure  representing  a 
horizontal  square  and  the  angle  of  inclination  increase  with  the 
distance  of  the  square  below  the  level  of  the  eye.  Fig.  14.  On 


FIG.  14.     VARIATION  OF  AREA  WITH  LEVEL 


the  left  in  Fig.  15  is  a  scale  of  levels  in  which  the  top  face  of  a 
one-inch  cube  is  represented  at  levels  one-half  inch  apart.  The 
numerals  indicate  the  distance  in  inches  of  the  front  corner  of 
each  square  below  the  horizon.  In  this  course  this  scale  will  be 
used  in  drawing  objects  at  different  levels. 

The  three  cubes  at  the  right  in  Fig.  15  show  an  application 
of  the  scale  in  representing  an  object  at  different  levels. 


PERSPECTIVE  SKETCHING 


25 


Vertical  Measurements.  All  vertical  distances  on  an  object 
should  be  measured  on  the  perspective  of  the  front  vertical 
edge  for  the  following  reasons : 


o    I 


FIG.  15.    SCALE  OF  LEVELS 


1.  The  front  vertical  edge  is  drawn  full  length. 

2.  In   general,   equal   vertical   distances   are   equal   in   per- 
spective only  when  measured  on  the  same  vertical  edge.    Exam- 
ple :  A  B  =  B  K  =  K  L.     Fig.  16. 


26 


MECHANICAL  DRAWING 


PERSPECTIVE  SKETCHING 


27 


Horizontal  Measurements.  All  horizontal  lengths  should  be 
estimated  by  drawing  the  faces  of  one-inch  cubes  so  that  they 
appear  to  be  squares. 

In  Fig.  16  lengths  A  D,  D  E,  E  G,  G  H,  and  H  I,  represent- 
ing equal  horizontal  distances,  are  measured  by  making  faces 
1,  2,  3,  4,  and  5  appear  as  squares. 

The  Enclosing  Solid.  An  imaginary  solid,  which  for  pur- 
'  poses  of  construction  is  made  to  circumscribe  an  object,  is  called 
an  enclosing  solid.  Fig.  17. 


FIG.  17.    ENCLOSING  SOLID 


The  Measure  Cube.  The  first  step  in  making  a  perspective 
sketch  is  to  draw  a  one-inch  cube  with  its  upper  front  cor- 
ner coincident  with  the  corresponding  corner  of  the  object 
or  its  enclosing  solid.  The  level  of  the  upper  face  of  the 
cube  is  determined  by  the  level  of  the  top  of  the  object. 
The  front  vertical  edge  of  the  cube  serves  as  the  vertical 
unit  of  measure  and  the  width  of  the  side  faces  as  the  hori- 
zontal unit  of  measure.  This  cube  is  therefore  called  the 
measure  cube. 

The  Table  Line.  When  an  object  rests  on  a  horizontal  sur- 
face its  position  with  reference  to  that  surface  is  shown  by  a 
horizontal  line  called  the  table  line.  The  position  of  this  line 
is  shown  in  Fig.  20.  It  should  be  drawn  freehand. 


28  MECHANICAL  DEAWING 

DATA  FOR  PLATE   2 

Given :  The  dimensioned  perspective  sketch  of  a  plate 
washer.  Fig.  20. 

Required :  To  make  a  sketch  of  the  plate  washer,  full  size, 
omitting  all  dimensions  and  lettering. 

Instructions : 

1.  Draw   the  border   rectangle   as   in    Plate    1.      Here    and 
throughout  the  constructive  stage  use  the  5H  pencil. 

2.  To   locate   the   center   of   the   sheet   proceed    as   follows : 
Place  the  edge  of  the  pencil  in  the  position  of  one  of  the  diago- 
nals of  the  border  line  rectangle.     Lift  the  pencil  and  draw  a 
part   of  the   diagonal   ne'ar  the   center  of  the   sheet.     In  like 
manner  draw  a  part  of  the  other  diagonal.     The  intersecting 
lines  will  locate  the  center  of  the  sheet. 

3.  Draw  the  measure  cube  with  its  upper  front  corner  A  at 
the  center  of  the  sheet  and  3J"  below  the  level  of  the  eye.    Fig. 

18.  Refer  to  the  angle  of  inclination  in  Fig.  15  for  the  re- 
quired level.    Eeproduce  this  angle  as  illustrated  in  Fig.  12. 

4.  Complete  the  enclosing  solid  by  drawing  the  lines  in  the 
order  indicated  by  the  numerals.     Fig.  18.     Measure  vertically 
and  to  the  right  and  left  as  previously  described  under  vertical 
and  horizontal  measurements,  respectively,  pages  25  and  27. 

5.  To  sketch  the  groove  through  the  plate  washer  locate  B, 
•J"  below  A,  and  draw  line  10,  converging  with  line  3,  Fig. 

19.  Lay   off  from  A   on  line  3   a  distance   representing  \". 
The   principle   of   foreshortening  applied  here   will  make   this 
distance  slightly  greater  than  one-half  of  A  D'.    Draw  line  11. 
In  the  same  manner  locate  and  draw  line  12.     Draw  line  13 
converging  with  line  2.     This  completes  the  constructive  stage. 

6.  Erase  all  lines  except  the  outline  of  the  figure  and  retrace 
the  sketch  with  a  carefully  sharpened  3H  pencil.    Draw  a  table 
line  as  in  Fig.  20. 

7.  Write  the  plate  number  and  name  in  the  lower  right  hand 
corner  of  the  sheet  and  press  the  paper  back  into  the  thumb 
tack  holes  as  directed  in  Plate  1. 


PERSPECTIVE  SKETCHING 


29 


FIG.  18.     CONSTRUCTIVE  STAGE.     ENCLOSING  SOLID 


FIG.  19.    CONSTRUCTIVE  STAGE  COMPLETE 


FIG.  20.    PLATE  WASHER.    FINISHED  SKETCH 


30  MECHANICAL  DRAWING 

DATA  FOE  EXTRA  PLATE 

Given:     A  dimensioned  perspective  sketch  of  an  Equalizer 
Safety  Block.    Fig.  21. 

Required :     To  make  a  sketch  of  the  Equalizer  Safety  Block, 
full  size,  omitting  all  dimensions. 

The  upper  front  corner  of  the  enclosing  solid  is  in  the  center 
of  the  sheet  and  3J"  below  the  level  of  the  eye. 


FIG.  21.     EQUALIZER  SAFETY  BLOCK 


ANGULAR  OBJECTS 

PREPAEATOEY    INSTRUCTIONS   FOR   PLATE    3 

To  Center  a  Perspective  Sketch.  It  is  essential  that  the  fin- 
ished sketch  be  centrally  located  on  the  sheet.  To  accomplish 
this  the  student  should  use  considerable  care  in  locating  the 
upper  front  corner  of  the  measure  cube.  Some  idea  of  the 
position  of  this  point  may  be  had  by  comparing  the  dimensions 
of  the  object  which  are  to  be  laid  off  to  the  right  and  left,  and 
by  taking  into  account  the  height  of  the  object  and  the  level 
at  which  it  is  drawn.  If  at  any  time  during  the  constructive 
stage  it  becomes  evident  that  the  sketch  is  not  centrally  located 
determine  the  correct  position  of  the  measure  cube,  erase  all 
lines,  and  proceed  as  before. 


PERSPECTIVE  SKETCHING 


31 


FIG.   22.     ENCLOSING  SOLID 


FIG.  23.     CONSTRUCTIVE  STAGE  COMPLETE 


FIG.  24.     JOURNAL  Box  WEDGE.     FINISHED  SKETCH 


32  MECHANICAL  DRAWING 

DATA   FOR   PLATE   3 

Given:  The  dimensioned  perspective  sketch  of  a  Journal 
Box  Wedge  with  the  upper  surfaces  5"  below  the  level  of  the 
eye.  Fig.  24. 

Required :  To  draw  the  Journal  Box  Wedge,  full  size,  with 
the  upper  surfaces  3^"  below  the  level  of  the  eye.  This  object 
introduces  inclined  surfaces. 

Instructions: 

1.  Locate  the  upper  front  corner  of  the  measure  cube  A, 
Fig.  22,  a  short  distance  above  and  to  the  left  of  the  center  of 
the  sheet. 

2.  Complete  the  enclosing  solid  as  in  Plate  2,  taking  care  to 
secure  the  necessary  convergence. 

3.  To  sketch  the  groove  in  the  Journal  Box  Wedge,  locate 
a  point  I"  below  A,   Fig.  23,   and  draw  B   H.    A  P  is  the 
edge  of  the  measure   cube  and  therefore  represents  one  inch. 
Make  D  Q  represent  one  inch  and  draw  vertical  lines  through 
P  and  Q  to  intercept  the  line  through  B  in  G  and  H.    Lay  off 
A  F  and  D  E  to  represent  three-eighths  of  an  inch  and  join  E  H 
and  F  G.     To  locate  point  K  on  the  farther  end  of  the  wedge 
draw  Q  0,  meeting  M  N  in  0.     The  vertical  line  through  O 
strikes  the  line,  vanishing  from  H  in  K. 

4.  Draw  the  horizontal  line  through  K  vanishing  to  the  left. 

5.  Sketch  in  all  remaining  lines  necessary  to  complete  the 
drawing.    This  completes  the  constructive  stage. 

6.  Finish  the  sketch  in  the  usual  manner. 


DATA  FOR  EXTRA  PLATE 

Given :  The  dimensioned  sketch  of  a  Bracket,  Fig.  25,  with 
the  upper  surface  of  the  enclosing  solid  2J"  below  the  level  of 
the  eye. 


PERSPECTIVE  SKETCHING 


33 


Required:     To  draw  the  Bracket,  full  size,  with  the  top  sur- 
face of  the  enclosing  solid  3^"  below  the  level  of  the  eye. 


FIG.  25.     BRACKET 


CYLINDRICAL   OBJECTS 
PREPARATORY    INSTRUCTIONS    FOR    PLATE    4 

The  Vertical  Measure  Cylinder.  As  stated  before,  the  cube 
is  the  basic  form  for  the  perspective  sketching  in  this  course. 
Fig.  26  shows  a  cylinder  inscribed  in  a  measure  cube.  The 
cylinder  is  therefore  one  inch  in  diameter  and  one  inch  long. 
The  principle  of  foreshortening  makes  the  axis  of  the  cylinder 
and  the  major  axis  of  each  of  the  ellipses  representing  its  bases 
slightly  less  than  one  inch.  In  sketching,  these  differences  may 
be  ignored.  In  Fig.  27  these  distances  are  one  inch  in  length. 

The  following  is  an  analysis  of  a  cylinder  which  will  be 
referred  to  as  the  vertical  measure  cylinder: 

1.  The  distance  between  the  center  of  the  ellipses  is  equal 
to  their  major  axes  or  one  inch.  A  B  =  C  C'  =  D  D'. 


34 


MECHANICAL  DRAWING 


2.  The  major  axes  C  C'  and  D  D'  of  the  ellipses  are  at  right 
angles  with  the  axis  of  the  cylinder. 

3.  The  minor  axes  E  E'  and  F  F'  are  coincident  with  the 
axis  of  the  cylinder. 

4.  Due  to  the  difference  in  level  the  minor  axis  F  F'  of  the 
lower  ellipse  is  greater  than  the  minor  axis  E  E'  of  the  upper 
ellipse.    Having  given  the  upper  ellipse,  the  half  length  of  the 
minor  axis  of  the  lower  ellipse  may  be  determined  by  drawing 
F  H'  through  D',  converging  with  E  H. 


FIG.    26.     VERTICAL    CYLINDER    IN-      FIG.    27.     VERTICAL    MEASURE    CY- 
SCRIBED  IN  A  MEASURE  CUBE  LINDER 

A  Scale  of  Levels.  The  left  half  of  Fig.  28  is  a  scale  of 
levels  showing  the  upper  base  of  a  measure  cube  at  levels  one- 
half  inch  apart.  It  is  evident  that  the  area  and  minor  axis  of 
the  ellipse  increase  with  the  distance  of  the  ellipse  below  the  level 
of  the  eye.  The  numerals  indicate  the  distance  of  the  center  of 
each  circle  below  the  horizon. 

The  three  cylinders  in  Fig.  28  show  an  application  of  the 
scale  to  the  sketching  of  vertical  cylinders  at  different  levels. 

To  Draw  and  Test  an  Ellipse  Representing  a  One-inch  Circle: 

1.  Draw  light  indefinite  lines  at  right  angles  to  each  other 
to  represent  the  axes  of  the  ellipse. 

2.  On  the  line  representing  the  major  axis  lay  off  on  either 
side  of  the  intersection  of  the  axes  one-half  the  diameter  of  the 
circle. 

3.  Refer  to  the  scale  of  levels;  estimate  and  lay  off  the  minor 
axis. 


PERSPECTIVE  SKETCHING 


35 


4.  Sketch  the  ellipse  lightly,  comparing  the  form  with  the 
corresponding  ellipse  in  the  scale  of  levels.  Care  should  be 
taken  to  avoid  sharp  or  blunt  ends. 


HORIZON 


•4  <= 


c 


FIG.  28.     SCALE  OF  LEVELS 

5.  Ordinary  defects  in  the  form  of  the  ellipse  will  be  evident 
if  the  sheet  is  turned  to  the  right,  to  the  left,  and  upside  down. 
A  further  test  recommended  is  as  follows:  Locate  A  and  B  on 
the  axis  equidistant  from  0.  Fig.  29.  The  vertical  distances 
from  these  points  to  the  ellipse  should  be  equal.  Compare  these 
distances  and  make  the  necessary  corrections.  Likewise  locate 


36 


MECHANICAL  DRAWING 


C  and  D  equidistant  from  0  and  compare  the  vertical  distances 
from  these  points  to  the  ellipse.  Make  the  necessary  corrections 
as  before. 


FIG.  29.     TESTING  AN  ELLIPSE 

Concentric  Circles  in  Perspective.  Fig.  30  shows  two  ellipses 
inscribed  in  concentric  squares.  The  ellipses  therefore  represent 
circles.  On  account  of  foreshortening,  the  axes  of  the  ellipses 
do  not  coincide  with  the  line  representing  the  diameter  of  the 


FIG.  30.    CONCENTRIC  CIRCLES  IN  PERSPECTIVE 

circles  or  with  each  other.  In  most  cases  the  difference  is  so 
slight  that  it  may  be  ignored.  In  this  course  when  ellipses  rep- 
resenting concentric  circles  are  to  be  drawn  their  major  axes 
will  be  made  coincident  unless  attention  is  called  to  conditions 


FIG.  31.     CONCENTRIC  CIRCLES  IN  HORIZONTAL  PLANE 

which  require  the  construction  shown  in  Fig.  30.  In  Figs.  31 
and  32  the  major  axis  C  F  is  laid  off  equal  to  the  diameter  of 
the  circle  as  in  the  case  of  the  ellipse  representing  the  one-inch 
circle.  Fig.  27.  A  one-inch  ellipse  should  be  drawn  first  and 


PERSPECTIVE  SKETCHING 


37 


tested.  The  half  length  of  the  minor  axis  of  a  larger  or  smaller 
ellipse  may  be  drawn  as  shown  in  Figs.  31  and  32.  C  D  is 
drawn  through  C  parallel  to  A  B. 

DATA  FOE  PLATE  4 

Given:  The  dimensions  of  a  Bushing,  which  consists  of  a 
hollow  cylinder,  outside  diameter  2",  inside  diameter  1", 
length  3". 

Required :  A  perspective  sketch  of  the  Bushing  with  its  axis 
vertical  and  the  upper  base  2J"  below  the  level  of  the  eye. 


FIG,  32.     CONCENTRIC  CIRCLES  IN  A  VERTICAL  PLANE 

Instructions: 

1.  Draw  through  the  center  of  the  sheet  a  vertical  line  to 
represent  the  axis  of  the  cylinder. 

2.  Through  points  H"  above  and  below  the  center  of  the 
sheet  draw  horizontal  lines  as  the  major  axes  of  the  ellipses 
representing  the  ends  of  the  bushing.     The  minor  axes   will 
coincide    with    the    axis    of    the    cylinder.      Care    should    be 
taken  to  make  the  angle  between  these  axes  a  right  angle. 

3.  Draw  the  ellipse  representing  the  smaller  circle  in  the 
upper  end  of  the  bushing  at  the  required  level.     Refer  to  the 


38  MECHANICAL  DRAWING 

scale  of  levels  to  estimate  the  major  and  minor  axes  of  the 
ellipse.  Draw  the  ellipse  with  these  axes  and  test  it  as  described 
under,  "To  Draw  and  Test  an  Ellipse,"  page  34. 

4.  Lay  off  the  major  axis  and  determine  the  length  of  the 
minor  axis  of  the  large  ellipse  as  described  under,  "Concentric 
Circles  in  Perspective,"  page  36. 

5.  Only  one-half  of  the  larger  ellipse  representing  the  lower 
end  of  the  bushing  will  be  seen.    The  length  of  the  minor  axis  of 
this  ellipse  may  be  found  by  the  method  illustrated  in  Fig.  27. 
While  only  the  lower  half  of  the  ellipse  will  be   needed,  the 
complete  ellipse  should  be  drawn  as  construction. 

6.  Complete  the  constructive  stage  of  the  sketch  by  drawing 
the  vertical  contour  elements  of  the  cylinder,  joining  the  ends 
of  the  major  axes  of  the  large  ellipses. 

7.  Erase  all  construction  lines  and  complete  the  sketch  in 
the  usual  manner. 

DATA    FOR    EXTRA    PLATE 

Given :  The  dimensions  of  a  washer  which  in  form  is  a  disc 
with  a  round  hole  through  it.  Outside  diameter  4",  inside 
diameter  2",  thickness  §". 

Required :  To  draw  the  washer  with  its  axis  vertical,  and  its 
upper  surface  four  inches  below  the  level  of  the  eye.  At  this 
level  a  portion  of  the  bottom  of  the  hole  will  be  visible. 

PREPARATORY    INSTRUCTIONS    FOR    PLATE    5 

The  Horizontal  Measure  Cylinder.  Fig.  33  shows  a  hori- 
zontal cylinder  inscribed  in  a  measure  cube.  This  cylinder  is 
therefore  one  inch  in  diameter  and  one  inch  long.  Due  to 
foreshortening,  the  major  axis  of  the  nearer  base  is  slightly 
less  than  one  inch,  and  the  axis  of  the  cylinder  is  shorter  than 
the  line  representing  the  horizontal  edge  of  the  measure 
cube. 

These  differences  are  so  slight  that  they  will  be  disregarded 
in  the  following  analysis  of  the  cylinder,  which  will  hereafter 
be  referred  to  as  the  horizontal  measure  cylinder.  Fig.  34. 


PERSPECTIVE  SKETCHING 


39 


Figs.  35  and  36  are  similar  to  Figs.  33  and  34,  respectively, 
and  show  a  horizontal  cylinder  at  a  different  level  with  its  axis 
receding  to  the  right  instead  of  to  the  left. 


FIG.  33.     HORIZONTAL  CYLINDER  IN- 
SCRIBED IN  A  MEASURE  CUBE 


FIG.  34. 


HORIZONTAL  MEASURE  CY- 
LINDER 


1.  The  distance  between  the  centers  of  the  bases  is  equal  to 
the  horizontal  receding  edge  of  the  measure  cube.  For  sketch- 
ing purposes  this  may  be  made  three-fourths  the  length  of  the 
major  axis  of  the  nearer  base. 


FIG.  35.     HORIZONTAL  CYLINDER  IN- 
SCRIBED IN  A  MEASURE  CUBE 


FIG.  36.     HORIZONTAL  MEASURE  CY- 
LINDER 


2.  The  major  axes  of  the  bases  are  perpendicular  to,  and 
the  minor  axes  coincident  with,  the  axis  of  the  cylinder  as  in 
the  vertical  measure  cylinder. 

3.  The  major  axis  of  the  nearer  base  is  equal  in  length  to 
the  diameter  of  the  cylinder,  or  one  inch.    The  major  axis  of  the 


40  MECHANICAL  DRAWING 

farther  base  is  shorter,  on  account  of  the  convergence  of  the 
contour  elements  of  the  cylinder. 

4.  When  the  nearer  ellipse  is  drawn,  the  half  length  of  the 
minor  axis  of  the  farther  ellipse  may  be  determined  by  drawing 
a  line  C  D  through  D,  converging  with  A  B.    Fig.  34. 

5.  Since  the  axis  of  a  horizontal   cylinder  always  extends 
toward  a  vanishing  point,  the  inclination  of  the  axis  determines 
the  level  at  which  a  cylinder  is  drawn.    Figs.  34  and  36. 

DATA  FOR  PLATE  5 

Given :     The  Bushing  represented  in  Plate  4. 
Required:     To  draw  the  Bushing  in  a  horizontal  position 
with  its  axis  4J"  below  the  level  of  the  eye. 

Instructions: 

1.  Draw  through  the  center  of  the  sheet  a  line  in  the  direc- 
tion of  one  of  the  vanishing  points,  to  represent  the  axis  of  the 
cylinder  at  the  required  level.    The  angle  of  inclination  may  be 
obtained  from  Fig.  15. 

2.  From  any  point  on  this  line  lay  off  three  foreshortened 
inches  referring  to  Fig.  16.    Mark  off  one-half  of  this  length  on 
each  side  of  the  center  of  the  sheet. 

3.  Draw  through  the  points  thus  determined  the  major  axes 
of  the  bases  at  right  angles  to  the  axis  of  the  cylinder. 

4.  Draw   the   ellipses   representing   the   nearer   end   of   the 
Bushing,  as  shown  in  Fig.  32.     Test  each  ellipse  as  described 
under  "To  Draw  and  Test  an  Ellipse,"  page  34. 

5.  From  the  ends  of  the  major  axis  of  the  larger  ellipse  draw 
contour  elements  converging  with  the  axis  of  the  cylinder  to 
determine  the  ends  of  the  major  axis  of  the  farther  base. 

6.  The  half  length  of  the  minor  axis  of  the  farther  base  may 
be  determined  as  shown  in  Figs.  34  and  36.    While  only  one-half 
of  the  farther  ellipse  will  show  in  the  finished  drawing,  a  better 
result   will   be   obtained   by   drawing   the   complete    ellipse    as 
construction. 

7.  Erase  all  construction  lines,  and  finish  the  sketch  in  the 
usual  manner. 


PERSPECTIVE  SKETCHING 


41 


DATA    FOR   EXTRA    PLATE 

Given :  The  dimensions  of  a  washer,  which  consists  of  a  disc 
with  a  round  hole  through  it.  Outside  diameter,  4";  inside 
diameter,  2" ;  thickness,  f". 

Required:  To  draw  the  washer  with  the  axes  of  the  cyl- 
inders horizontal  and  3"  below  the  level  of  the  eye.  Atten- 
tion is  called  to  the  fact  that  a  portion  of  the  farther  end  of  the 
hole  will  be  visible. 


FIG.  37.     DRAWING  A  CUBE  AT  ANY  ANGLE 


EXTENSION  OF  PERSPECTIVE  THEORY 
PREPARATORY    INSTRUCTIONS    FOR    EXTRA    PLATES 

The  Measure  Cube  in  New  Positions.  In  the  preceding  plates 
the  measure  cube  was  drawn  at  different  levels,  but  always  with 
its  side  faces  at  45°  with  the  horizon. 

If  the  measure  cube  is  turned  with  its  side  faces  making 
other  angles  with  the  horizon,  the  number  of  positions  in  which 
an  object  may  be  drawn  will  be  increased. 

Fig.  37  shows  a  method  of  constructing  a  measure  cube  at 
any  level  and  with  its  side  faces  at  any  desired  angle.  The 
steps  in  the  construction  are  as  follows : 

1.  Draw  an  ellipse  representing  a  two-inch  circle  at  the 
required  level. 


42 


MECHANICAL  DRAWING 


2.  Draw  a  semi-circle  of  the  same   diameter  as  the  circle 

represented  by  the  ellipse  with  its  center  at  the  center  of  the 
ellipse. 

3.  Mark  off  on  the  semi-circle  the  angles  which  the  faces  of 
the  cube  are  to  make  with  the  horizon.    These  angles  should  be 
90°  apart. 

4.  Vertical  lines  through  these  points  intercept  the  ellipse 
in  the  ends  of  the  nearer  edges  of  the  upper  face  of  the  cube. 
These  edges  meet  at  the  center  of  the  ellipse  which  is  the  upper 
front  corner  of  the  cube. 


FIG.  38.     CYLINDER  INSCRIBED  IN  A 
MEASURE  CUBE 


FIG.  39.     MEASURE  CYLINDER 


5.  Make  the   front  vertical  edge   one   inch  long  as  in   45° 
perspective. 

6.  Complete  the  cube  by  drawing  the  remaining  edges  con- 
verging so  as  to  give  the  faces  of  the  cube  the  appearance  of 
squares.     It  will  be  noted  that  the  farther  edges  of  the  upper 
face  intersect  on  the  line  making  45°   with  each  of  the  side 
faces. 

The  Measure  Cylinder  in  New  Positions.  Fig.  38  shows  a 
horizontal  cylinder  inscribed  in  a  measure  cube  with  its  side 
faces  at  other  than  45°  to  the  horizon.  This  cylinder  is  there- 
fore one  inch  in  diameter  and  one  inch  long.  Due  to  foreshort- 
ening, the  major  axis  of  the  nearer  base  is  slightly  less  than  one 
inch  and  the  axis  of  the  cylinder  is  shorter  than  the  line  rep- 
resenting the  horizontal  edge  of  the  measure  cube.  These  differ- 


PERSPECTIVE  SKETCHING 


43 


ences  are  so  slight  that  they  will  be  disregarded  in  the  following 
analysis  of  the  measure  cylinder.     Fig.  39. 

1.  The  distance  between  the  centers  of  the  bases  is  equal  to 
the  horizontal  receding  edge  of  the  measure  cube.    This  distance 
will  be  shorter  as  the  angle  of  the  axis  of  the  cylinder  to  the 
horizon  increases. 

2.  The  major  axis  of  the  bases  are  perpendicular  to,  and  the 
minor  axis  coincident  with,  the  axis  of  the  cylinder. 

3.  The  major  axis  of  the  nearer  base  is  equal  in  length  to 
the  diameter  of  the  cylinder,  or  one  inch.     The  major  axis  of 


FIG.  40.     CYLINDER  INSCRIBED  IN  A 
MEASURE  CUBE 


PIG.  41.     MEASURE  CYLINDER 


the  farther  base  is  shorter  011  account  of  the  convergence  of  the 
contour  elements  of  the  cylinder. 

4.  The  length  of  the  minor  axis  of  the  nearer  base  will 
depend  upon  the  angle  that  the  axis  of  the  cylinder  makes  with 
the  horizon.  Fig.  39  illustrates  the  case  in  which  the  minor 
axis  is  lengthened,  due  to  the  axis  of  the  cylinder  making  an 
angle  greater  than  45°  with  the  horizon.  Fig.  41  illustrates  the 
case  in  which  the  minor  axis  is  shortened,  due  to  the  axis  of  the 
cylinder  making  an  angle  less  than  45°  with  the  horizon.  The 
length  of  the  minor  axis  for  other  positions  may  be  estimated 
by  using  Figs.  39  and  41  as  guides.  For  any  angle  the  axis  of 
the  cylinder  makes  with  the  horizon  the  length  of  the  minor 


44 


MECHANICAL  DRAWING 


FIG.  42.    SILL  FILLING  PIECE 


FIG.  43.     DRILL  JIG 


FIG.  44.     SCREW  BEARING  CAP 


PERSPECTIVE  SKETCHING 


45 


axis  will  remain  the  same  for  all  levels.  When  the  nearer 
ellipse  is  drawn,  the  half  length  of  the  minor  axis  of  the  farther 
base  may  be  determined  by  drawing  a  line  C  D  through  D, 
converging  with  A  B.  Figs.  39  and  41. 

DATA   FOR   EXTRA   PLATE 

Given:     The  objects  shown  in  Figs.  42,  43,  44,  and  45. 

Required:  To  draw  one  or  more  of  the  above  objects  in 
positions  selected  from  the  following  table  by  the  instructor. 
The  level  at  which  the  object  is  drawn  may  be  assumed  by  the 
student. 


FIG.  45.     DRILL  JIG 

The  right  vertical  face  of  the  enclosing  solid  makes  one  of 
the  following  angles  with  the  horizon : 

1.  15°. 

2.  30°. 

3.  60°. 

4.  75°. 

The  objects  should  be  centered  on  the  sheet  as  in  previous 
problems. 


46  MECHANICAL  DRAWING 

SUMMARY 

It  has  been  the  aim  of  this  chapter  to  develop  in  a  condensed 
but  thorough  manner  the  essential  principles  upon  which  per- 
spective sketching  is  based.  Furthermore,  the  presentation  is 
intended  to  assist  the  student  to  develop  a  fair  degree  of  skill  in 
drawing  perspectives  of  rectangular,  angular,  and  cylindrical 
objects.  He  should  now  be  able  to  draw  objects  composed  of  a 
combination  of  these  elementary  forms.  It  is  hoped  that  the 
student  will  have  gained  confidence  in  his  ability  to  visualize  and 
represent  an  object  pictorially.  If  this  has  been  accomplished  he 
will  find  a  use  for  perspective  as  an  interpretation  of  orthographic 
drawing  which  will  be  treated  in  the  succeeding  chapters. 

As  a  means  of  reviewing  Chapter  I  the  following  questions 
and  problems  are  given : 

REVIEW  QUESTIONS 

1.  (a)   What  is  the  horizon?      (b)    How  is  it  represented? 
(c)  What  is  its  relation  to  the  eye? 

2.  (a)  What  is  a  vanishing  point?     (b)  Where  is  it  located? 

3.  Where   do   parallel   horizontal   lines   appear  to   meet   in 
perspective  ? 

4.  Do  vertical  lines  appear  to  converge  in  perspective  ? 

5.  (a)  What  is  meant  by  foreshortening?     (b)  Are  the  per- 
spectives of   equal  lengths   on  the   same   vertical   edge   equal? 
(c)    On  the  same  horizontal  edge?      (d)   Are  the  perspectives 
of  equal  vertical  lengths  at  different  distances  from  the  observer 
equal  ? 

6.  (a)  What  is  the  angle  of  inclination?     (b)  How  does  it 
vary? 

7.  (a)  The  paper  is  fastened  in  what  position  on  the  draw- 
ing board?     (b)  How  is  it  fastened? 

8.  Describe  in  detail  how  the  pencil  should  be  sharpened 
for  sketching. 

9.  (a)  What  is  the  position  of  the  hand  and  pencil  in  sketch- 
ing  horizontal   lines?     (b)   Vertical   lines?     (c)   What   is   the 


PERSPECTIVE  SKETCHING 


47 


essential  difference  ?     (d)   What  movements  are  made  to  produce 
the  line? 

10.   (a)   What  is  meant  by  constructive  stage?     (b)   Finish- 
ing stage? 


FIG.    46.     FRAME 


11.  In  what  way  does  a  scale  of  levels  assist  in  making  a 
perspective  of  a  rectangular  object? 

12.  (a)  Where  are  all  vertical  measurements  laid  off  in  per- 
spective?    (b)   Why? 


FIG.  47.     BRACE 

13.  How  are  horizontal  measurements  made  ? 

14.  Explain  what  is  meant  by  enclosing  solid. 

15.  (a)   What  is  a  measure  cube?     (b)   Why  is  it  called  a 
measure  cube  ? 

16.  Of  what  use  is  the  table  line  ? 


48 


MECHANICAL  DRAWING 


17.  (a)   How  do  you  proceed  to  locate  the  drawing  centrally 
on  the  sheet  ? 

18.  How  are  the  perspectives  of  the  inclined  lines  located? 


FIG.  48.    CLUTCH  JAW 


FIG.  49.     SOLID  Box 


19.  (a)  Give  the  proportions  of  the  vertical  measure  cyl- 
inder, (b)  The  major  axes  of  the  bases  are  at  what  angle  with 
the  axis  of  the  cylinder? 


PERSPECTIVE  SKETCHING  49 

20.  How  does  the  difference  in  level  affect  the  appearance  of 
a  horizontal  circle  in  perspective? 

21.  Of  what  assistance  is  a  scale  of  levels  in  drawing  a  ver- 
tical cylinder? 

22.  How  is  the  ratio  of  the  minor  axes  of  two  ellipses  repre- 
senting concentric  circles  determined? 

23.  (a)   Give  the  proportions  of  a  horizontal  measure  cyl- 
inder,    (b)   The  major  axes  of  the  bases  are  at  what  angle  with 
the  axis  of  the  cylinder?     (c)   What  is  the  relative  length  of  the 
major  and  minor  axes  of  the  nearer  base  ? 

DATA  FOR  REVIEW  PROBLEMS 

Given:     The  object  shown  in  Figs.  46,  47,  48,  49. 

Required:  To  draw  one  or  more  of  the  above  objects  in  45° 
perspective.  The  level  at  which  the  object  is  drawn  may  be 
assumed  by  the  student. 


CHAPTER  II 

ORTHOGRAPHIC  SKETCHING 
PREPARATORY   INSTRUCTIONS   FOR    PLATE    6 

Views.  In  perspective  sketching  the  object  was  viewed  from 
one  position,  so  chosen  as  to  show  its  three  general  dimensions 
in  one  view.  Such  a  sketch  does  not  show  the  principal  edges 
of  the  object  in  their  true  lengths. 

In  order  to  represent  the  principal  edges  of  an  object  in 
their  true  lengths,  it  is  usually  viewed  in  two  or  more  directions, 
viz.;  from  directly  in  front,  directly  above,  or  directly  from 
the  right  or  left.  Views  thus  secured  are  known  as  ortho- 
graphic. In  engineering  drawing  orthographic  views  are  gen- 
erally used. 

Fig.  52  shows  two  views  of  a  Chafing  Plate.  The  view 
marked  top  represents  orthographically  what  is  seen  from  di- 
rectly above  the  object  and  the  view  marked  front  represents 
what  is  seen  from  directly  in  front  of  the  object.  The  top  view 
shows  two  general  dimensions  in  horizontal  directions,  viz.; 
from  left  to  right  and  from  front  to  back.  The  front  view 
shows  the  horizontal  dimension  from  left  to  right  and  the 
vertical  dimension.  Thus  the  three  dimensions  are  given  in 
the  two  views  and  the  proportions  of  the  object  are  deter- 
mined. 

Relation  of  Top  and  Front  Views.  For  convenience  in 
making  and  interpreting  the  drawing  it  is  essential  that  the 
top  view  always  be  placed  directly  above  the  front  view. 
Under  this  condition  all  distances  from  left  to  right  may  be 
projected  from  one  view  to  the  other. 

"Reading"  the  Drawing.  To  form  a  mental  image  of  an 
object  the  relation  of  its  surfaces,  edges,  and  corners  as 
represented  must  be  studied.  This  process  is  called  reading 
the  drawing  and  is  illustrated  under  the  four  following 
headings : 

50 


FIG.  50.     TYPE  PROBLEM — PERSPECTIVE  OF  CHAFING  PLATE 


FIG.  51.    TYPE  PROBLEM 
CONSTRUCTIVE  STAGE  OF  THE  ORTHOGRAPHIC  SKETCH 


52 


MECHANICAL  DRAWING 


Plane  Surfaces.  Fig.  52  represents  an  object  having  plane 
surfaces. 

1.  When  the  observer  is  looking  perpendicularly  at  a  sur- 
face it  shows  in  its  true  form  and  size.  Example:  The  rectan- 
gular top  surface  A  B  C  D  of  the  Chafing  Plate,  Fig.  52,  is 
represented  in  its  true  form  and  size  in  the  top  view. 


c 

K      C 

.1 

OJ 

[ 

T          •      ^~ 

. 

i 

ft 

E 

TOP 

I 

I" 

= 
*°                                                                                                                                           I         1 

G 

LJ^T           UH 

3-1-            4'-           ,k? 

J                       J4                        la    • 

FRONT 

«wn  ^£>™. 

FIG.  52.     TYPE  PROBLEM — FINISHED  SKETCH  OF  CHAFING  PLATE 


2.  When  the  observer  is  looking  edgewise  at  a  surface  it 
appears  as  a  straight  line.  Example :  Line  E  F  is  the  front 
view  of  the  top  surface  A  B  C  D,  Fig.  52. 

Straight  Edges.  1.  A  straight  edge  viewed  at  right  angles 
to  its  length  shows  as  a  line  in  its  true  length.  Example :  The 
front  edge  of  the  top  surface  of  the  Chafing  Plate  shows  in  its 
true  length  in  the  top  view  and  in  the  front  view  in  lines  A  B 
and  E  F  respectively. 

2.  A  straight  edge  viewed  endwise  appears  as  a  point. 
Example :  Point  F  is  the  front  view  of  the  edge  B  C.  Fig.  52. 


ORTHOGRAPHIC  SKETCHING 


53 


Corners.  1.  A  corner  shows  as  a  point  when  viewed  from 
any  direction.  Example :  The  upper  front  corner  at  the  right 
of  the  Chafing  Plate  is  represented  by  B  in  the  top  view  and  F 
in  the  front  view. 

Invisible  Edges.  Hidden  edges  or  surfaces  are  represented 
by  dotted  lines  to  distinguish  them  from  visible  edges,  or  sur- 
faces. Example:  K  J  in  the  top  view,  Fig.  52. 

PROBLEMS  AND  QUESTIONS  ON  ORTHOGRAPHIC  PRINCIPLES 

The  student  should  test  his  knowledge  of  the  orthographic 
principles  just  stated  by  answering  the  following  questions: 
See  Fig.  53. 


9  10  II 

TOP 


FRONT 

FIG.  53.     KEVIEW  PROBLEM 


1.  (a)   Where  is  the  front  view  of  the  horizontal  surface  9, 
10,  15,  16?     (b)   Of  10,  12,  13,  15?     (c)   Of  9,  11,  14,  16? 

2.  (a)   Where  is  the  top  view  of  the  horizontal  surface  5,  4? 
(b)   Of  8,  1? 

3.  (a)  Where  is  the  top  view  of  the  front  vertical  surface 
1,  2,  3,  4,  5,  6,  7,  8?     (b)   Of  the  rear  vertical  surface  1,  2,  3, 
4,  5,  6,  7,  8? 


54  MECHANICAL  DRAWING 

4.  (a)   Where  is  the  top  view  of  the  vertical  surface  7,  8? 
(b)   Of  3,  4?     (c)   Of  5,  6? 

5.  (a)   Where  is  the  top  view  of  the  front  horizontal  edge 
2,  3?     (b)   Of  7,  6? 

6.  (a)   Where  is  the  front  view  of  the  rear  horizontal  edge 
15,  13?     (b)   Of  16,  14? 

7.  (a)   Where   is    the   front   view   of   the   upper   horizontal 
edge  10,  15?     (b)   Of  12,  13? 

8.  (a)  Where  is  the  top  view  of  the  edge  5?     (b)   Of  6? 

9.  (a)   Where  is  the  front  view  of  the  upper  front  corner 
12?     (b)   Of  9?     (c)   Of  the  upper  back  corner  15? 

10.  (a)   Where    is    the    top    view    of   the    front   corner    2? 
(b)   Of  5? 

The  Type  Problem.  In  each  of  the  following  problems  pre- 
sented for  solution  the  methods  to  be  employed  and  the  results 
to  be  obtained  will  be  illustrated  by  a  type  problem.  This 
type  problem  will  consist  of  two  parts : 

1.  A  drawing  of  an  object  similar  to,  and  represented  in  the 
same  manner  as,  the  one  given  for  solution. 

2.  A  solution  of  the  problem  corresponding  to  that  required. 

Example:  Fig.  52  is  the  type  problem  for  the  first  ortho- 
graphic sketch.  Fig.  50  is  the  perspective  made  from  Fig.  52 
corresponding  to  the  one  the  student  will  make  from  Fig. 
54  or  55. 

Materials.  The  materials  used  for  the  plates  in  this  chap- 
ter are  the  same  as  those  used  in  perspective  sketching  (see 
page  17)  except  that  in  this  case  the  5H  pencil  will  be  used 
for  both  the  constructive  and  finishing  stages. 

Perspective  Sketches.  In  this  chapter  perspective  sketches 
will  be  drawn  preceding  the  orthographic  sketches  as  a  means 
of  interpreting  the  orthographic  views  and  at  the  same  time  to 
continue  the  practice  necessary  to  develop  skill  in  representing 
objects  in  perspective. 


I 

1 

.1 
T 

I 

r-ico 


FIG.  54.     SPRING  STEM  GUIDE 


FIG.  55.     BRACE 


(55) 


56  MECHANICAL  DRAWING 

DATA  FOR  PLATE   6 

Given:     An  orthographic  sketch,  Fig.  54  or  55. 

Required:  To  draw  a  45°  perspective  sketch  of  the  object 
shown  in  Fig.  54  or  55  as  assigned  by  the  instructor,  with  the 
upper  front  corner  of  the  enclosing  solid  3J"  below  the  level 
of  the  eye.  Use  the  corner  marked  A  as  the  upper  front  corner 
of  the  object.  Omit  all  dimensions. 


PREPARATORY    INSTRUCTIONS    FOR    PLATE    7 

Constructive  Stage.  In  this  stage  all  lines  should  be  drawn 
light  and  full.  In  laying  out  the  views  of  an  orthographic 
sketch  on  the  sheet  proceed  in  the  following  manner: 

1.  Referring  to  Fig.  51,  mark  off  tentatively  the  position  of 
the  extreme  right  and  left  of  each  view.     Shift  both  marks  to 
the  right  or  to  the  left,  if  necessary,  to  make  A  equal  B. 

2.  In  like  manner  mark  off  the  vertical  dimension  of  each 
view,   leaving   a  space  between  the  two  views  proportional  to 
that  which  is  shown  in  the  figure.    This  distance  should  be  from 
f "  to  1".     Shift  all  marks  up  or  down,  if  necessary,  to  make 
C  equal  D. 

3.  Make  any  necessary  adjustments  in  the  general  propor- 
tion of  the  views. 

4.  In  proportioning  the  details  of  the  views  a  comparison 
of  the  dimensions  of  each  detail  with  the  dimensions  of  the  views 
in  which  it  appears  will  aid  in  securing  good  results.     Example : 
In  the  front  view,  Fig.  52,  the  height  of  the  opening  is  five- 
eighths  of  the  total  height  of  the  view,  and  its  length  is  slightly 
more  than  four-fifths  of  the  length  of  the  view. 

Finishing  Stage.  1.  All  construction  lines  should  be  erased 
and  the  lines  of  the  drawing  retraced,  using  the  5H  pencil. 

2.  Invisible  edges  should  now  be  represented  by  dotted  lines, 
which  are  composed  of  |"  dashes  with  sV'  spaces  between  them. 


ORTHOGRAPHIC  SKETCHING 


57 


Fig.  56  shows  the  correct  method  of  joining  dotted  lines  to  full 
lines. 

Arrangement  of  Dimensions.  When  detail  dimensions  and 
a  dimension  representing  their  sum  are  given,  they  should  be 
grouped  in  parallel  lines.  The  shorter  dimensions  should  be 
near  the  outline  of  the  object  to  avoid  confusion  arising  from 
the  crossing  of  extension  and  dimension  lines.  Example :  Those 
below  the  front  view,  Fig.  52,  are  properly  arranged. 

The  Dimension  Form.  The  dimension  form  consists  of  the 
numerals  designating  feet  and  inches,  the  foot  and  inch  marks, 
the  dash,  the  dimension  and  extension  lines,  and  the  arrowheads 
as  arranged  in  Fig.  193. 


T 

T 

(L 

^ 

\ 

} 

t 

i — ! 


i 


FIG.  56.    DOTTED  LINES 


It  will  be  seen  that  the  arrowheads  are  placed  on  the  dimen- 
sion lines  with  their  points  touching  the  extension  lines.  They 
are  composed  of  two  slightly  curved  lines  symmetrical  with 
respect  to  the  dimension  line.  The  length  of  the  arrowhead 
should  be  about  J"  and  the  width  Ty.  Fig.  193.  The  strokes 
for  arrowheads  pointing  in  different  directions  are  shown  in 
Fig.  194. 

Horizontal  dimensions  should  be  read  with  the  observer  at 
the  bottom  of  the  sheet.  Vertical  dimensions  should  be  read 
with  the  observer  at  the  right  of  the  sheet. 

Whole  Numbers  and  Fractions.  The  whole  number  in  a 
dimension  will  be  made  one-eighth  inch  high. 

The  total  height  of  the  fraction  should  be  twice  the  height 
of  the  whole  number  with  a  clear  space  between  each  numeral 


58  MECHANICAL  DRAWING 

and  the  division  line.  Fig.  196.  To  check  these  heights  mark 
off  an  eighth-inch  and  a  quarter-inch  space  on  the  edge  of  a 
card  and  use  it  as  a  scale. 

Extension  lines  should  begin  about  gV'  from  the  outline 
of  the  object  and  should  continue  to  about  |"  beyond  the 
arrowhead. 

The  space  between  the  outline  of  the  object  and  the  nearest 
dimension  line  or  between  two  parallel  consecutive  dimension 
lines  should  be  about  \" . 

DATA  TOE  PLATE  7 

Given:     Orthographic  sketches,  Figs.  54  and  55. 

Required:  To  make  the  orthographic  sketch  shown  in  Fig. 
54  or  55  to  an  enlarged  scale. 

Instructions:  1.  Draw  a  border  line  as  in  perspective 
sketching. 

2.  Proportion  the  views  and  locate  them  centrally  on  the 
sheet  as  previously  explained. 

3.  Draw  in  the  details  and  finish  the  drawing  as  usual. 

4.  Arrange  the  dimensions  as  shown,  keeping  in  mind  the 
points  mentioned  under  "Dimensioning,"  page  57. 

PREPARATORY    INSTRUCTIONS    FOR    PLATE    8 

Relation  of  Front  and  Side  Views.  As  previously  explained, 
an  observer  sees  all  vertical  dimensions  and  the  horizontal  dimen- 
sions from  right  to  left  in  the  front  view.  All  vertical  dimen- 
sions and  the  horizontal  dimension  from  front  to  back  are  seen 
in  the  side  view.  For  convenience  in  making  and  reading  the 
drawing  the  right  side  view  is  placed  to  the  right  of  the  front 
view,  when  only  these  two  are  drawn.  In  like  manner  the  left 
side  view  is  placed  to  the  left  of  the  front  view.  In  either  case 
all  vertical  distances  may  be  projected  from  one  view  to  the 
other.  Fig.  57  shows  the  front  and  two  side  views  of  an  object 
in  their  proper  relative  positions. 


ORTHOGRAPHIC  SKETCHING        '.  59 

Since  the  two  side  views  convey  the  same  information,  if  one 
is  given  the  other  may  be  drawn.  The  essential  difference 
between  the  side  views  is  that  in  one,  parts  of  the  object  may 
be  concealed  while  in  the  other  they  are  visible.  Example :  In 
Fig.  57,  A  B  is  invisible  from  the  left  and  visible  from  the  right. 
When  this  is  the  case  usually  the  better  solution  is  to  draw  the 
view  in  which  as  few  hidden  lines  as  possible  are  represented. 

Inclined  Surface.  A  plane  surface  of  an  object  which  is 
neither  horizontal  nor  vertical  is  called  an  inclined  surface. 
Fig.  57  represents  an  object  having  inclined  surfaces.  If  the 
surface  is  rectangular  and  two  of  its  edges  are  at  right  angles 
to  the  direction  in  which  it  is  viewed,  as  C  D  E  F  in  Fig.  57, 


LEFT   END  FRONT  RIGHT   END 

FIG.  57.     RELATION  OF  FRONT  AND  SIDE  VIEWS 

the  vertical  dimension  of  the  rectangle  representing  the  surface 
in  the  front  view  is  less  than  the  actual  width  of  the  surface. 

The  inclined  surface  C  D  E  F  is  represented  by  the  inclined 
line  G  H  in  the  left  side  view.  G  H  is  equal  to  the  true  width  of 
the  surface.  G'  H',  representing  the  same  surface  in  the  right 
side  view,  is  also  equal  to  the  true  width  of  the  surface.  It  is 
evident  that  the  front  view  of  the  object  shows  the  true  length 
of  the  inclined  surface  and  the  side  view  its  true  width. 

Inclined  Edges.  A  straight  edge  which  is  not  at  right  angles 
to  the  direction  in  which  it  is  viewed  is  represented  by  a  line 
shorter  than  the  actual  length  of  the  edge. 

Example :  The  line  E  C  in  Fig.  57  is  shorter  than  the  edge 
of  the  inclined  surface  which  it  represents. 

In  the  side  view  this  line  is  viewed  in  a  direction  at  right 
angles  to  it  and  therefore  shows  in  its  true  length  in  G  H. 

The  student  should  test  his  knowledge  of  the  orthographic 
principles  just  stated  by  answering  the  following  questions: 


60 


MECHANICAL  DRAWING 


PROBLEMS  AND  QUESTIONS  IN  ORTHOGRAPHIC  PRINCIPLES 
Refer  to  Fig.  58. 

1.  Where  is  the  side  view  of  the  inclined  surface  1,  2,  7,  8? 

2.  (a)  Is  line  1,  2  equal  to  the  true  width  of  the  inclined 
surface?     (b)   Where  is  its  true  length  shown?     (c)   Why? 

3.  Where  is  the  inclined  edge  1,  8  shown  in  its  true  length  ? 
Why? 


10  9 

LEFT  SIDE  FRONT 

FIG.   58.    REVIEW   PROBLEM 

4.  (a)   Is  the  vertical  surface  11,  15  on  the  front  or  back  of 
the  object?     (b)   Why?     (c)   Where  is  it  shown  in  the  front 
view? 

5.  Where  is  the  vertical  surface  14,  13  shown  in  the  front 
view? 

6.  Where  is  the  horizontal  surface  13,  16  shown  in  the  front 
view  ? 

7.  Where  is  the  horizontal  surface  6,  7  shown  in  the  side  view  ? 

8.  Where  is  the  vertical  surface  4,  9  shown  in  the  side  view  ? 

In  sketching  an  angle  where  the  dimension  is  given  in  degrees 
the  ends  of  the  inclined  line  should  be  located  by  estimating  the 
length  of  the  legs  of  the  right  triangle  of  which  the  inclined 
line  is  the  hypotenuse.  Example:  See  Fig.  59. 

In  determining  the  position  of  a  line  passing  through  an 


ORTHOGRAPHIC  SKETCHING 


61 


invisible   corner  make   a   construction   for  the   invisible   corner 
as  shown  in  Fig.  59. 


FIG.  59.     CONSTRUCTION  FOR  ANGLES  AND  HIDDEN  CORNERS 
DATA  FOR   PLATE   8 

Given:     Orthographic  sketches,  Figs.  63  and  64. 
Required:     To  draw  a  45°  perspective  sketch  of  the  object 
shown  in  Fig.  63  or  64  as  assigned  by  the  instructor.     The 


TIG.  60.    TYPE  PROBLEM — GIVEN  VIEWS 

upper  front  corner  of  the  enclosing  solid  is  3^"  below  the  level 
of  the  eye.  Use  the  point  marked  A  as  the  upper  corner  of  the 
measure  cube.  Omit  all  dimensions. 


FIG.  61.     TYPE  PROBLEM — PERSPECTIVE  SKETCH 


Kf 


a 


'-A 

Vjcvi      I     f 


FIG.  62.     TYPE  PROBLEM — REQUIRED  VIEWS 


(62) 


VTT 


\N!9 


" 


FIG.  63.     DOVETAIL  CROSS  SLIDE 


FRONT 


FIG.  64.     DOUBLE  DOVETAIL 


(63) 


64  MECHANICAL  DRAWING 

PREPARATORY    INSTRUCTIONS    FOR    PLATE    9 

Dimensioning  Angles.  An  angle  may  be  dimensioned  in 
degrees  as  in  Fig.  62.  In  this  case  the  dimension  line  is  an  arc 
with  its  center  at  the  intersection  of  the  two  lines  forming  the 
angle.  An  angle  is  sometimes  dimensioned,  as  in  the  case  of 
the  grooves  through  the  object  in  Fig.  62,  where  the  widths  at 
the  top  and  bottom  of  the  groove  are  given. 


DATA  FOR   PLATE   9 

Given:  Orthographic  sketches,  Figs.  63  and  64,  showing  the 
front  and  left  side  of  each  of  the  objects. 

Required:  To  draw  the  front  and  right  side  views  of  the 
object  shown  in  Fig.  63  or  64  as  assigned  by  the  instructor. 

Instructions:  1.  Block  in  the  views  of  the  object  as  in  Plate  7 
so  that  they  are  in  the  center  of  the  sheet. 

2.  Complete  the  details  of  the  views  in  light"  line. 

3.  Trace  over  the  lines,  making  them  the  proper  weight. 

4.  Draw  the  dimension  lines  and  put  in  the  arrowheads  and 
figures.     The    dimensions   on   this    plate   should   be   placed   in 
positions  similar  to  those  in  the  type  problem,  Fig.  62. 

5.  "Write  in  the  plate  number  and  name  as  usual.     Press  the 
paper  back  into  the  tack  holes. 


PREPARATORY    INSTRUCTIONS   FOR   PLATE    10 

Cylindrical  Surfaces.  Fig.  65  represents  an  object  having 
cylindrical  surfaces.  When  viewed  in  a  direction  at  right 
angles  to  the  axis  of  the  cylinder  a  cylindrical  surface  appears 
as  a  rectangle.  Two  of  the  sides  of  the  rectangle  represent  the 
circular  bases  of  the  cylinder  and  are  therefore  equal  in  length 
to  its  diameter.  They  represent  the  bases  of  the  cylinder 
viewed  edgewise.  Example :  A  B  and  C  D,  Fig.  65.  The  other 
two  sides  of  the  rectangle  represent  the  contour  elements,  or 
the  elements  which  divide  the  visible  part  of  the  surface  from 
that  which  is  invisible.  Example :  A  C  and  B  D,  Fig.  65. 


FIG.  65.     TYPE  PROBLEM — GIVEN  VIEWS  OF  SHAFT  COUPLING 


QJtaAu 


FIG.  66.     TYPE  PROBLEM — PERSPECTIVE  OF  SHAFT  COUPLING       (65) 


66  MECHANICAL  DRAWING 

When  the  observer  is  looking  in  the  direction  of  the  axis  of 
a  cylinder  the  cylindrical  surface  is  seen  edgewise  and  appears 
as  a  circle.  Example :  E  F  G  H,  Fig.  65. 

Circular  Edges.  A  circular  edge  viewed  in  a  direction  at 
right  angles  to  its  plane  show's  as  a  true  circle.  Example : 
E  F  G  H  in  Fig.  65. 

A  circular  edge  viewed  in  the  direction  of  its  plane  shows 
as  a  straight  line  equal  in  length  to  the  diameter  of  the  circle. 
Example:  A  B  and  C  D  in  Fig.  65. 

The  student  should*  test  his  knowledge  of  the  orthographic 
principles  just  mentioned  by  answering  the  following  questions : 
See  Fig.  70. 


FIG.  67.     QUARTER  SECTION  ILLUSTRATED  IN  PERSPECTIVE 

1.  (a)   Where  is  the  left  end  view  of  the  cylindrical  surface 
3,  4,  11,  12?     (b)  Of  1,  2,  13,  14? 

2.  Where  is  the  front  view  of  the  cylindrical  surface  25, 
26,  27,  28? 

3.  (a)  Where  is  the  circular  surface  1,  16,  14,  15,  shown  in 
the  end  view?     (b)  Where  is  the  surface  2,  3,  12,  13  shown  in 
the  end  view? 


PIG.  68.    TYPE  PROBLEM — CONSTRUCTIVE  STAGE  OF  THE  ORTHOGRAPHIC  SKETCH 


FIG.  69.     TYPE  PROBLEM — FINISHED  SKETCH  OF  THE  SHAFT  COUPLING  (67) 


68 


MECHANICAL  DRAWING 


4.  (a)   Where  is  the  circular  edge  6,  9  shown  in  the  end 
view?     (b)  Where  is  the  circular  edge  4,  11  shown  in  the  end 
view  ? 

5.  What  surface  would  be  crosshatched  if  a  quarter  section 
were  made  cutting  on  the  lines  0,  17  and  0,  18  ? 


DATA  FOR  PLATE   10 

Given:     Orthographic  sketches,  Figs.  71  and  72. 

Required:  To  draw  a  perspective  of  the  object  shown  in 
Fig.  71  or  72  as  assigned  by  the  instructor,  with  its  axis  ver- 
tical. The  upper  end  of  the  object  is  2J"  below  the  level  of 
the  eye. 

PREPARATORY   INSTRUCTIONS   TOR   PLATE   11 

Quarter  Sections.  A  drawing  can  often  be  made  much 
clearer  by  representing  the  object  with  a  portion  of  it  removed. 


19  .  14         13  10         9 

LEFT    END  FRONT 

FIG.  70.    REVIEW  PROBLEM 

One  of  the  chief  advantages  is  the  reduction  of  dotted  lines. 
Sections  are  usually  taken  by  considering  the  object  cut  through 
an  axis  of  symmetry.  A  view  which  shows  the  object  cut  into 
the  center  on  two  planes  at  right  angles  to  each  other  is  called 
a  quarter  section.  Example :  In  Fig.  69  the  front  view  is  shown 
in  quarter  section.  In  drawing  the  front  view  the  quarter 


ORTHOGRAPHIC  SKETCHING  69 

A  O  B  (end  view)  is  supposed  to  be  removed.  It  should  be 
noted  that  the  end  view  represents  the  complete  object. 

Crosshatching.  The  cut  surface  in  the  section  view  is  rep- 
resented conventionally  by  crosshatcking  which  consists  of  very 
fine  parallel  lines,  equally  spaced.  In  this  problem  the  lines 
should  be  drawn  -fa"  apart  and  at  an  angle  of  45°  with  the 
horizontal. 

Center  Lines.  A  line  which  represents  an  axis  of  symmetry 
is  called  a  center  line.  Center  lines  may  be  straight  or  curved. 
Of  the  straight  lines  there  are  two  classes,  principal  and  second- 
ary. A  principal  center  line  is  one  about  which  the  entire  view 
is  symmetrical.  Example :  A  C  in  Fig.  69.  The  principal  cen- 
ter lines  should  extend  about  \"  beyond  the  outline  of  the 
view.  A  secondary  center  line  is  one  about  which  only  part 
of  the  view  is  symmetrical.  Example :  E  F,  Fig.  69,  is  the  center 
line  for  the  hole  only.  Secondary  center  lines  should  extend 
about  J"  beyond  the  outline  of  the  part  of  which  they  represent 
the  axes. 

A  circular  center  line  usually  passes  through  the  centers  of 
a  number  of  holes  grouped  at  a  certain  distance  from  a  central 
point.  It  is  not  quite  a  complete  circle.  Example :  See  left  end 
view.  Fig.  69. 

In  general,  every  circle  must  have  two  center  lines  at  right 
angles  to  each  other.  When  one  of  the  center  lines  is  circular 
the  other  is  therefore  radial.  Example :  See  Fig.  71. 

Dimensioning  Cylindrical  Surfaces  and  Circles.  The  diam- 
eter of  the  cylinder  may  be  given  by  placing  the  dimension  on 
a  diameter  of  the  circle  representing  the  cylindrical  surface. 
Example :  See  Fig.  69.  It  may  be  given  between  extension  lines 
drawn  from  the  rectangular  view.  Example :  See  Fig.  69.  In 
this  case  the  dimension  figures  should  be  followed  by  a  D  or 
Diam  to  indicate  that  the  dimension  is  a  diameter.  A  hole  to  be 
drilled,  cored,  or  bored  may  be  indicated  by  printing  the  word, 
showing  how  it  is  to  be  obtained  or  finished,  together  with  the 
dimension  and  arrow  pointing  to  the  hole.  The  word  and  the 
dimension  should  be  placed  in  an  open  area  near  the  hole  rep- 
resented. The  line  drawn  under  the  word  should  be  about  3^" 
below  the  letters.  Example:  See  Fig.  69. 


3" 


RIGHT    END 


FIG.  71.     TRUNNION  BEARING 


RIGHT    END 


PIG.  72.     SPRING  CASING  BASE 


(70) 


ORTHOGRAPHIC  SKETCHING  71 

To  Sketch  a  Circle.  Draw  two  light  lines  at  right  angles 
arid  lay  off  a  length  equal  to  the  radius  on  each,  measuring  out 
from  their  intersection.  Sketch  in  the  circle  through  the  four 
points  thus  located.  If  the  circle  is  large,  draw  radial  lines  at 
45°  with  those  previously  drawn  and  lay  off  points  as  before. 

DATA  FOE  PLATE  11 

Given:  Orthographic  sketches,  Figs.  71  and  72  showing  the 
front  and  right  end  views. 

Required :  To  draw  the  front  quarter  section  and  left  end 
views  of  the  objects.  Fig.  71  or  72  as  assigned  by  the  instructor. 

Instructions: 

1.  Proportion  the  views  on  the  plate. 

2.  Draw  the   principal  center  lines   for   the   circular  view. 
Draw  the  circles  in  the  following  order:   (1)  The  larger  circles. 
(2)    Circular   center   line.     (3)    The    circles   representing    the 
small  holes. 

3.  To  draw  the  rectangular  view,  first  determine  its  vertical 
dimension   by   projecting   from   the   end   view.     Complete   the 
view. 

4.  Retrace  the  lines  as  in  the  finishing  stage,  giving  particu- 
lar attention  to  those  affected  by  the  quarter  section. 

5.  Draw  in  extension  and  dimension  lines  and  put  in  the 
dimensions.     Finish  the  sketch  by  crossh  a  telling   the   cut  sur- 
faces.    Care  should  be  taken  to  make  the  section  lines  parallel 
to  each  other  and  at  45°  to  the  horizontal. 

SUMMARY 

In  this  chapter  the  work  of  the  preceding  chapter  has  been 
continued  in  order  that  the  value  of  the  perspective  sketch  as  an 
aid  in  interpreting  orthographic  views  might  be  apparent.  At 
the  same  time  more  general  application  has  been  made  of  per- 
spective principles  and  additional  skill  has  been  acquired  in  rep- 
resenting objects  pictorially. 

It  has  been  the  chief  aim  of  this  chapter  to  familiarize  the 


FIG.  73.    BEARING  CAP 


LEFT   SIDE 


FIG.  74.     VISE  JAW 


(72) 


t 


Jj 


RIGHT    SIDE 


FIG.  75.     TURNING  TOOL  HOLDER 


tEFT  SIDE 


FIG.  76.    VALVE  BONNET 


(73) 


74  MECHANICAL  DRAWING 

student  with  the  method  of  representation  generally  used  in 
engineering  drawing.  By  this  time  the  student  should  be  able 
to  read  drawings  of  ordinary  complexity  as  well  as  to  make 
freehand  orthographic  sketches  with  a  considerable  degree  of 
skill  and  confidence. 

As  a  means  of  reviewing  Chapter  II  the  following  questions 
and  problems  are  given: 

REVIEW  QUESTIONS 

1.  (a)   In  what  direction  does  one  look  at  an  object  in  mak- 
ing its  orthographic  views?     (b)   How  does  this  differ  from  the 
way  it  is  viewed  in  making  a  perspective  of  it  ? 

2.  (a)   How  many  general  dimensions  does  each  orthographic 
view  show?     (b)   How  many  orthographic  views  are  necessary 
to  show  three  general  dimensions? 

3.  (a)   What  is  the  position  of  the  top  with   reference  to 
the  front  view?     (b)   Why?     (c)   Which  general  dimension  is 
common  in  the  top  and  front  views  ? 

4.  What  is  meant  by  "Reading"  a  drawing? 

5.  (a)   Under  what  condition  does  a  surface  appear  as  a  line 
in  a  view?     (b)  When  a  hidden  surface  is  viewed  edgewise 
how  is  it  represented? 

6.  (a)   When  is  a  plane  surface  shown  in  its  true  form  in 
one  view  and  as  a  straight  line  in  the  other?     (b)   When  is  a 
plane  surface  shown  in  less  than  its  true  size  in  one  view  and 
as  a  straight  line  in  the  other? 

7.  (a)   When  is  a  cylindrical  surface  represented  as  a  rec- 
tangle in  one  view  and  as  a  circle  in  the  other?     (b)   When  is 
a  circular  surface  represented  as  a  straight  line  in  one  view  and 
as  a  circle  in  the  other  ? 

8.  (a)   When  is  a  straight  edge  of  an  object  shown  in  its  true 
length  in  two  views?     (b)   When  in  its  true  length  in  one  view 
and  as  a  point  in  the  other?     (c)   When  in  its  true  length  in  one 
view  and  in  less  than  its  true  length  in  the  other? 

9.  How  are  the  corners  of  an  object  represented? 

10.  Describe  the  process  of  proportioning  the  views  of  an 
object  and  locating  them  centrally  on  the  sheet. 


ORTHOGRAPHIC  SKETCHING  75 

11.  What  are  the  lengths  of  dashes  and  spaces  in  dotted 
lines  ? 

12.  (a)   Illustrate  by  a  sketch  how  detail  and  overall  dimen- 
sions are  grouped,     (b)  What  space  is  allowed  between  the  out- 
line of  the  object  and  the  nearest  dimension  line?     (c)   Between 
dimension  lines? 

13.  (a)   Where  is  the  right  side  view  placed  with  respect  to 
the  front  view?     (b)   Where  is  the  left  side  view  placed  with 
respect  to  the  front  view? 

14.  (a)   What  general  dimensions  of  an  object  are  shown  in 
the  right  side  view?     (b)   In  the  left  side  view? 

15.  What  determines  the   choice  between  a  right   and  left 
side  view? 

16.  (a)  Why  is  an  object  sometimes  shown  with  a  part  re- 
moved?    (b)   Define  quarter  section,     (c)   Is  the  part  cut  by 
the  section  planes  shown  as  removed  in  both  views? 

17.  (a)  What  is  the  purpose  of  crosshatching  ?     (b)   At  what 
angles   are   the   crosshatching  lines   drawn?     (c)    What  is  the 
usual  distance  between  crosshatching  lines? 

18.  (a)   What  is  a  principal  center  line?     (b)   A  secondary 
center  line? 

19.  (a)  When  is  a  straight  center  line  used?     (b)   Circular 
center  line? 

20.  (a)   How  many  center  lines  must  be   drawn   for   each 
circle?     (b)   At  what  angle  to  each  other? 

21.  Illustrate   how  the   two   views   of   a   cylinder   may   be 
dimensioned. 

DATA  FOR  REVIEW  PROBLEMS 

Given:     An  orthographic  sketch,  Fig.  73. 

Required:  To  make  the  orthographic  sketch  shown  in  Fig. 
73  to  an  enlarged  scale. 

Given:  An  orthographic  sketch,  Fig.  74,  showing  the  front 
and  left  side  views  of  the  object. 

Required:  To  draw  the  front  and  right  side  views  of  the 
object  shown  in  Fig.  74. 

Given:  An  orthographic  sketch,  Fig.  75,  showing  the  front 
and  right  side  views  of  the  object. 


76  MECHANICAL  DRAWING 

Required:  To  draw  the  front  and  left  side  views  of  the 
object  shown  in  Fig.  75. 

Given:  An  orthographic  sketch,  Fig.  76,  showing  the  front 
and  left  side  views  of  the  object. 

Required :  To  draw  the  front  quarter  section  and  right  side 
views  of  the  object  shown  in  Fig.  76. 


CHAPTER  HI 

PENCIL  MECHANICAL  DRAWING 
PREPARATORY  INSTRUCTIONS  FOR  PLATE  12 

Three  View  Problems.  While  in  most  cases  two  views  are 
sufficient  to  show  the  form  of  an  object,  some  objects  require 
three  views.  Example:  The  front  and  side  views  of  the  Drill 
Jig  Base  in  Fig.  77A  do  not  show  the  form  of  the  vertical 
groove.  Hence  a  top  view  is  necessary.  Also,  the. front  view 
is  required  to  show  the  V  groove  and  the  left  side  to  show  the 
T  slot. 

As  stated  under  Plate  8,  the  right  and  left  side  views  convey 
the  same  information  and  therefore  either  may  be  drawn.  The 
one  is  usually  selected  which  requires  the  fewer  dotted  lines. 
Example:  Comparing  Fig.  77,  A  and  B,  the  left  side  view  is 
preferable  for  this  reason.  Ordinarily  the  right  or  left  side 
view  is  drawn  opposite  the  front  view.  In  some  cases,  however, 
a  better  arrangement  will  be  secured  by  placing  the  side  view 
opposite  the  top  view  instead  of  opposite  the  front  view.  Fig. 
77,  C  and  D.  In  this  case  the  views  are  so  related  that  horizontal 
distances  from  front  to  back,  which  are  common  to  the  top  and 
side  views,  may  be  projected  from  one  view  to  the  other.  To 
relate  properly  the  side  view  to  the  front  view  of  an  object,  atten- 
tion should  be  given  to  the  following  condition.  In  all  cases  the 
side  views  of  the  front  surface  are  adjacent  to  the  front  view  of 
the  object.  Example:  M  N  and  0  P  in  Fig.  77  represent  the 
side  views  of  the  front  surface. 

The  student  should  test  his  knowledge  of  the  orthographic 
principles  just  stated  by  answering  the  following  questions: 
See  Fig.  78. 

1.  (a)  Why  is  the  top  view  of  the  object  necessary?  (b) 
The  front  view?  (c)  The  right  side  view? 

77 


78 


MECHANICAL  DRAWING 


2.  (a)   Is  the  right  side  view  preferable  to  the  left  side  view? 
(b)   Why? 

3.  (a)   Where  is  the  near  horizontal  edge  5    6  shown  in  the 
top  view?     (b)   In  the  front  view? 

4.  (a)   Where  is  the  vertical  surface  5,  8  shown  in  the  front 
view?     (b)   In  the  top  view? 


" 

. 

M 

i 
i 
i 

C  =r4 

J! 

1 

i 

J 

:_3~T 

"-  J  I 

i 
i 

r  3] 

_ 

, 

A 

B 

] 

ij 

ri 

1 

!  n 

g 

j 

~T 

j 

1 

r 

I 

J 

1 

r____-_-^4 

1 

J 

C 

D 

FIG.  77.     KELATION  OF  FRONT,  TOP,  AND  SIDE  VIEWS 


5.  (a)   Where  is  the  back  vertical  surface  1,  2,  3,  4  shown  in 
the  side  view?     (b)   In  the  top  view? 

6.  Draw  the  right  side  view  opposite  the  top  view. 

7.  Draw  the  left  side  view  opposite  the  front  view. 

8.  Draw  the  left  side  view  opposite  the  top  view. 

In  this  chapter  an  orthographic   sketch  will  precede  each 
mechanical  drawing.       This  will  develop  further  skill  in  ortho- 


PENCIL  MECHANICAL  DRAWING 


79 


graphic  sketching  and  will  make  the  student  familiar  with  the 
problem.  As  a  result,  time  will  be  saved  in  making  the 
mechanical  drawing. 


_J 


1 


1 

1 

i 

| 

1 

1 
1 

1 

J_ 

_L 

! 
i 

1 

1 

1 
\ 
1 

4.... 

1 

1 

1  —  '— 

1 

~J  —  T 

FIG.  78.    REVIEW  PROBLEM 
DATA  FOR  PLATE  12 

Given:     Perspective  sketches,  Figs.  82,  83,  and  84. 

Required:  To  draw  a  three  view  orthographic  sketch  of  the 
object  shown  in  Fig.  82,  83,  or  84  with  dimensions,  as  assigned 
by  the  instructor. 

Proceed  as  in  the  orthographic  sketching  in  Chapter  II. 


PREPARATORY  INSTRUCTIONS  FOR  PLATE  13 

The  following  is  a  list  of  materials  needed  in  making  the 
pencil  mechanical  drawings  in  this  chapter.  See  Chapter  V  for 
complete  description  of  each. 

1.  Drawing  board. 

2.  High  grade  paper  similar  to  Duplex  or  Cream,  11"  x  15" 
sheets. 

3.  T-square. 


80 


MECHANICAL  DRAWING 


FIG.    79.     TYPE   PROBLEM — PERSPECTIVE   OF  DRILL  JIG  BASE 


FIG.  80.     TYPE  PROBLEM — CONSTRUCTIVE  STAGE  OF  THE  PENCIL  MECHANICAL 

DRAWING 


82 


MECHANICAL  DRAWING 


FIG.   82.     CLAMP   FOR   TENSION  WEIGHING   FIXTURE 
ONE  WANTED — CAST  IRON 


2    BORE  THR1 


FIG.  83.     YOKE  BLOCK  FOR  LOCOMOTIVE  VALVE  MOTION 
ONE  WANTED — CAST  IRON 


PENCIL  MECHANICAL  DRAWING  83 

4.  30°-60°  and  45°  triangles. 

5.  High  grade  5H  pencil. 

6.  Scale. 

7.  Bow  compass. 

8.  4H  compass  lead. 

9.  Pencil  pointer. 

10.  Eraser. 

11.  Erasing  shield. 

The  T-square  should  be  placed  with  the  head  against  the  left 
edge  of  the  drawing  board  and  held  firmly  in  place  with  the 


FIG.  84.    ANGLE  FOR  TENSION  WEIGHING  FIXTURE 
ONE  WANTED — CAST  IRON 

left  hand  as  shown  in  Fig.  86.  All  horizontal  lines  are  ruled 
along  its  upper  edge. 

The  Drawing  Paper  should  be  fastened  to  the  board  in  the 
same  position  as  for  sketching.  After  inserting  the  first  tack 
make  the  upper  edge  of  the  sheet  horizontal  by  means  of  the 
T-square ;  stretch  the  sheet  and  insert  the  remaining  thumb  tacks 
in  the  usual  manner. 

The  5H  pencil  should  be  sharpened  at  both  ends.  One  end 
is  used  for  ruling  lines  and  the  other  for  laying  off  measure- 
ments. The  ruling  point  is  obtained  by  cutting  away  the  wood 
to  expose  about  J"  of  lead  and  by  rubbing  opposite  sides  of  the 
lead  on  a  sandpaper  pad  or  file  to  oroduce  a  wedge-shaped 


84 


MECHANICAL  DRAWING 


point.  Fig.  85.  This  point  is  used  for  ruling  continuous  lines. 
The  measuring  point  is  similar  to  the  conical  point  used  in 
sketching  except  that  the  point  is  sharper  in  order  that  very 
accurate  measurements  may  be  laid  off  with  it.  It  is  used 


RULING    POINT 


MEASURING    POINT 


FIG.  85.    EULING  AND  MEASURING  POINTS  OF  THE  MECHANICAL  DRAWING 

PENCIL 

both  for  measuring  and  making  dotted  lines.  All  measurements 
on  this  plate  should  be  laid  off  from  the  edge  of  the  scale,  gradu- 
ated to  inches  and  sixteenths.  To  insure  accuracy  the  eye 
should  be  directly  above  the  division  on  the  scale  from  which 


FIG.  86.    EULING  A  HORIZONTAL  LINE 


the  dimension  is  to  be  laid  off.  Care  should  be  taken  to  place 
the  point  of  the  pencil  on  the  paper  exactly  opposite  the  mark 
on  the  scale.  The  pencil  should  be  revolved  upon  its  axis  while 


PENCIL  MECHANICAL  DRAWING 


85 


in  this  position  without  pressing  the  lead  into  the  paper.  The 
mark  left  by  the  pencil  should  be  a  small,  round  dot  just  visible 
to  the  eye. 

Ruling  Horizontal  Lines.  In  ruling  horizontal  lines  the  posi- 
tion of  the  hand  is  the  same  as  for  sketching  horizontal  lines. 
In  this  case,  however,  the  pencil  is  held  leaning  slightly  for- 
ward with  the  point  in  the  position  shown  in  Fig.  86.  The  line 
is  drawn  with  a  continuous  motion  to  the  right  with  the  tip 
of  the  fourth  finger  touching  the  T-square  to  steady  the  hand. 
Fig.  86.  The  forearm  should  always  be  at  right  angles  with 
the  line  being  drawn. 


FIG.  87.    RULING  A  VERTICAL  LINE 


Vertical  Lines  are  drawn  along  the  edge  of  a  triangle  which  is 
set  against  the  T-square  as  shown  in  Fig.  87.  Note  that  the 
triangle  is  to  the  right  of  the  line.  The  line  should  be  drawn 
away  from  the  T-square  with  the  hand  and  arm  in  the  same 
relative  position  to  the  line  being  drawn  as  for  horizontal  lines. 

In  using  the  bow  compass  proceed  in  the  following  manner: 

1.  Sharpen  the  lead  to  a  narrow  wedge  in  width  about  one- 
half  the  diameter  of  the  lead. 

2.  Set  the  lead  so  that  it  projects  about  one-half  the  length 
of  the  needle  point  beyond  the  shoulder. 


86  MECHANICAL  DRAWING 

3.  Draw  the  center  lines  of  the  circle  to  be  drawn  at  right 
angles  and  lay  off  the  radius  on  one  of  them. 

4.  Grasp  the  compass  by  the  handle  between  the  thumb  and 
first  finger  of  the  right  hand.     Care  should  be  taken  to  place  the 
needle  point  exactly  at  the  intersection  of  the  center  lines. 

5.  Adjust  the  lead  to  the  exact  radius  and  draw  the  circle, 
rolling  the  handle  of  the  compass  between  the  thumb  and  finger. 
Fig.  88. 

When  erasing  lines  which  are  very  close  to  or  joining  re- 
quired lines,  the  erasing  shield  should  be  used.     The  shield  pro- 


FIG.  88.     DRAWING  A  CIRCLE  WITH  THE  Bow  COMPASS 

tects  the  required  lines  and  thus  the  time  lost  in  retracing  them 
is  avoided. 

The  Border  Rectangle.     To  draw  the  border  rectangle  pro- 
ceed as  follows: 

1.  Lay  off  J"  from  the  upper  and  left-hand  edges  of  the 
sheet. 

2.  Through  the  points  thus  located  draw  the  upper  and  left- 
hand  sides  of  the  border  rectangle. 

3.  On  these  lines  and  from  their  intersection  lay  off  14"  to 
the  right  and  10"  downward. 

4.  Through  the  points  thus  found  draw  the  remaining  sides 
of  the  border  rectangle. 

The  Enclosing  Rectangle.     In  mechanical  drawing  the  views 
are  located  centrally  by  calculating  the  position  of  a  rectangle 


PENCIL  MECHANICAL  DRAWING 


87 


in  which  they  may  be  inscribed.  In  this  course  the  distance 
between  views  should  not  be  less  than  f"  or  more  than  V. 
The  student's  calculation  should  be  made  as  indicated  in  Fig.  89. 


14 "  = 


J 

** 

t 

•i 
% 

X 

I 

N 

^-  Border  JL/ne 
fEnc/05/ng  Recfang/e 

• 

*               7  ".,-.          >. 

,* 

J"        . 

<  J         J  >  --                   't- 
N 

1 

FIG.  89.    CALCULATION  FOR  THE  SIZE  AND  POSITION  OF  THE  ENCLOSING 

RECTANGLE 


Accuracy.  It  is  of  prime  importance  that  a  mechanical 
drawing  be  accurate.  Accuracy  depends  both  upon  the  quality 
and  condition  of  the  instruments  and  materials  and  upon  the 


88  MECHANICAL  DRAWING 

skill  of  the  draftsman.  All  straight  edges,  angles,  etc.,  should 
be  tested  as  described  in  Chapter  V.  When  the  tools  are  found 
to  be  in  good  condition  the  draftsman  should  then  take  great 
care  to  lay  off  measurements  accurately,  and  draw  the  lines 
exactly  through  the  points  located. 

Errors  multiply  with  the  number  of  operations  involved, 
hence,  other  things  being  equal,  the  most  direct  construction  is 
the  most  accurate  one. 

Constructive  Stage.  In  this  stage  all  measurements  are  laid 
off  and  lines  drawn  lightly  and  of  indefinite  length.  As  many 
measurements  as  possible  should  be  made  while  the  scale  is 
being  used.  Whenever  practicable,  consecutive  measurements 
should  be  laid  off  with  the  scale  in  one  position.  The  lines 
should  be  drawn  long  enough  so  that  there  will  be  no  need  to 
extend  them. 

No  distinction  is  made  between  visible  and  invisible  edges 
in  this  stage. 

Finishing  Stage.  The  lines  not  needed  in  the  finished  draw- 
ing are  now  erased  and  the  required  lines  retraced  with  a  care- 
fully sharpened  pencil,  care  being  taken  to  make  them  of  uniform 
width  and  shade  and  to  end  them  at  the  proper  points.  The 
lines  should  be  drawn  in  the  following  order:  (1)  Horizontal 
lines  beginning  at  the  top  of  the  sheet.  (2)  Vertical  lines  begin- 
ning at  the  left  of  the  sheet.  The  hidden  edges  should  now 
be  represented  by  dotted  lines.  They  are  composed  of  -J" 
dashes  and  ^y  spaces.  Fig.  56.  The  end  of  each  dash  can  be 
made  distinct  by  keeping  the  end  of  the  pencil  in  contact  with 
the  paper  until  the  end  of  the  line  is  reached. 

Extension  and  Dimension  Lines.  As  in  orthographic  sketch- 
ing the  extension  lines  should  begin  about  gV'  from  the  outline 
of  the  object  and  continue  about  J"  beyond  the  arrowheads. 
The  space  between  the  outline  of  the  object  and  the  nearest 
dimension  line,  or  between  two  parallel  consecutive  dimension 
lines,  should  be  about  \".  The  extension  and  dimension  lines 
should  be  of  the  same  width  and  shade  as  the  object  lines.  Cen- 
ter lines  may  be  used  as  extension  lines,  but  not  as  dimension 
lines. 


PENCIL  MECHANICAL  DRAWING  89 

The  Dimension  Figures  should  be  of  the  same  height  as  those 
used  in  orthographic  sketching,  Fig.  196. 

Notes  are  used  to  explain  points  which  the  drawing  does  not 
make  clear.  They  usually  relate  to  materials,  finish,  number 
of  parts  needed,  etc.  Example :  See  note  below  the  view,  Fig.  81. 

The  Title.  The  views  of  an  object  with  their  dimensions 
and  notes  do  not  convey  all  of  the  necessary  information.  A 
title  which  supplies  the  deficiency  is'  therefore  added.  The 
title  is  usually  placed  in  the  lower  right-hand  corner  of  the 
sheet  so  that  it  will  be  easily  accessible  when  the  drawing  is 
filed.  The  titles  in  this  chapter  will  contain  the  name  of  the 
object,  the  name  of  the  machine  for  which  it  is  to  be  made,  the 
scale  to  which  it  is  to  be  drawn,  the  plate  number,  the  student's 
initials,  and  the  filing  number.  For  a  more  general  discussion  of 
the  contents  of  a  title  see  page  147.  The  relative  importance  of 
the  items  in  the  title  is  shown  by  varying  the  heights  of  the 
letters.  The  more  important  items  are  printed  in  larger  letters. 
The  words  for  each  title  in  this  chapter  will  be  given  below  the 
figure  from  which  the  drawing  is  made. 

The  Title  Block.  The  title  for  each  mechanical  drawing 
plate  in  this  course  will  be  placed  in  a  title  block.  The  dimen- 
sions of  this  block  with  the  height  of  each  line  of  letters  and  the 
positions  of  the  items  are  shown  in  Fig.  90. 

Balancing  a  Title.  It  is  essential  to  the  appearance  of  a  title 
that  the  lines  be  symmetrical  with  respect  to  a  vertical  center 
line.  Example :  Fig.  90  shows  a  title  properly  balanced. 

To  balance  the  title  proceed  as  follows : 

1.  Tack  a  piece  of  drawing  paper  to  the  board  opposite  the 
lower  right-hand  corner  of  the  sheet.     Fig.  90.     This  will  be 
referred  to  as  the  trial  sheet. 

2.  Draw  a  line  as  a  continuation  of  the  lower  border  line 
on  the  trial  sheet.    This  is  a  base  line  for  measurements. 

3.  Lay  off  on  the  trial  sheet  the  space  for  the  letters  as 
given  in  Fig.  90.     Extreme  accuracy  in  making  these  measure- 
ments is  necessary  as  the  width  of  the  letters  varies  with  their 


90 


MECHANICAL  DRAWING 


height.     A  small  error  in  height  makes  the  letter  appear  much 
too  large  or  too  small. 

4.  Rule  each  guide  line  on  the  trial  sheet  and  the  drawing 
sheet  with  one  setting  of  the  T-square.  Care  should  be  taken 
to  draw  exactly  through  the  points  located.  Check  the  heights 
of  the  spaces  with  the  scale. 


<                                       3  '  " 

^ 

O 

BACK 

F(j)R 

Z4"  TUF 

SCALE-FU 

O 

REST 

tREJT    LATHE 

LL  SIZE 

SPACES  ^' 

a 

1 

71 

5 

\K    BACK 

\\ 

\24     TURRE 

TT  LATHE—  g 

12     |    as  6  |  A.G.S. 

SCALE-FULL  SIZE 

[Mg^rglJ 

-  -1- 

\    TV 

STUDENTS     INITIALS 

\                 \   FILING 

NUMBER 

V  PLATE    NUMBER 

FIG.  90.     TITLE  BLOCK — SHOWING  A  METHOD  OF  BALANCING  THE  LINES  OF 

THE  TITLE 


5.  Letter  each  line  of  the  title  on  the  trial  sheet,  giving  atten- 
tion to  the  proportion  of  the  letters  and  to  spacing.     Do  not 
try  to  balance  the  lines  on  this  sheet. 

6.  Locate  the  middle  point  of  each  line  on  the  trial  sheet. 

7.  Draw  the  vertical  center  line  of  the  title  through  the  cen- 
ter of  the  title  rectangle. 

8.  Cut  out  each  line  of  letters  from  the  trial  sheet  and  place 
it  above  the  space  in  which  it  is  to  be  lettered  on  the  drawing 
sheet,  with  its  middle  point  on  the  center  line  of  the  title. 

9.  Letter  each  line,  following  the  spacing  on  the  trial  line. 
The  result  should  be  a  perfectly  balanced  title. 


PENCIL  MECHANICAL  DRAWING 


91 


DATA  FOR  PLATE  13 

Given:     The  orthographic  sketch,  Plate  12. 

Required:     To   make   a  pencil   mechanical   drawing   from 
Plate  12. 

Instructions:     1.  Test  the  drawing  board,  T-square,  and  tri- 
angles as  explained  in  Chapter  V. 

2.  Draw  the  border  line  as  previously  explained. 

3.  Calculate  the  size  of  the  enclosing  rectangle. 

4.  Lay  off  as  many  of  the  dimensions  of  the  object  as  pos- 
sible at  one  time.     Draw  the  lines  lightly. 


FIG.  91.     TYPE  PROBLEM— PERSPECTIVE  OF  CHAIN  SUPPORT 

5.  Check  the  drawing  for  accuracy. 

6.  Erase  unnecessary  lines  and  retrace  the  drawing,  taking 
care  to  end  the  lines  exactly  at  their  intersections.     Dot  the 
lines  representing  hidden  edges. 

7.  Draw  extension  and  dimension  lines  and  put  in  dimensions. 

8.  Letter  a  note,  giving  the  number  of  parts  required  and 
the  material  from  which  they  are  to  be  made. 

9.  Letter  the  title,  using  the  name  of  the  object  given  below 
the  figure  from  which  the  drawing  was  made. 


Jolt 

T 


PENCIL  MECHANICAL  DRAWING  93 

PREPARATORY   INSTRUCTIONS   TOR   PLATE    14 

Relation  of  Front  and  Side  Views.  In  all  cases  the  side 
views  of  the  front  surface  are  adjacent  to  the  front  view  of  the 
object.  Example :  A  B,  Fig.  92,  represents  the  side  view  of 
the  front  surface  of  the  chain  support. 

Dimensioning  Angles.  The  direction  of  inclined  lines  is 
given  in  two  ways.  The  more  common  method  is  by  coordinates 
as  shown  in  Fig.  92.  Another  method  less  frequently  used  is 
shown  in  Fig.  62.  When  an  angle  is  dimensioned  in  degrees  the 
dimension  line  is  an  arc  with  its  center  at  the  intersection  of 
the  lines  forming  the  angle. 

DATA  FOR  PLATE  14 

Given:     Perspective  sketches,  Figs.  93,  94,  and  95. 

Required :  To  draw  a  two  view  orthographic  sketch  of  the 
object  shown  in  Fig.  93,  .94,  or  95  with  dimensions,  as  assigned 
by  the  instructor. 

Instructions:  Proceed  as  in  orthographic  sketching,  Chap- 
ter II. 

PREPARATORY    INSTRUCTIONS   FOR    PLATE    15 

Inclined  Lines.  When  inclined  lines  make  an  angle  of  30°, 
45°,  or  60°  they  may  be  drawn  along  the  edge  of  one  of  the 
triangles  in  combination  with  the  T-square.  Angles  of  15°  and 
75°  may  be  obtained  by  a  combination  of  the  two  triangles  and 
the  T-square.  See  Chapter  V  for  detailed  discussion. 

Scale.  When  an  object  is  too  large  to  be  drawn  full  size  on 
the  sheet  it  may  be  drawn  to  some  fraction  of  its  actual  size.  Half 
and  quarter  size  are  common  scales  for  drawing  machine 
parts.  The  edge  of  the  scale,  graduated  to  read  half  or  quarter 
size,  should  be  used  instead  of  dividing  the  dimensions  by  2  or  4. 

DATA  FOR  PLATE  15 

Given:     The  orthographic  sketch,  Plate  14. 
Required:     To   make   a   pencil   mechanical   drawing   from 
Plate  14.     (Draw  the  Journal  Bearing,  Fig.  95,  half  size.) 


94 


MECHANICAL  DRAWING 


Instructions:  1.  Draw  the  border  line  and  calculate  the  size 
of  the  enclosing  rectangle  as  in  Plate  13. 


FIG.  93.     FOUNDATION  WASHER  FOR  CORLISS  ENGINE  BED 
TWELVE   WANTED — CAST   IRON 


FIG.   94.     BACK  REST  FOR   TWENTY-FOUR-INCH   TURRET  LATHE 
FOUR  WANTED — CAST  IRON 


2.  Lay  off  the  dimensions  of  the  object  and  complete  the  con- 
structive stage. 

3.  Check  carefully  each  dimension  for  accuracy. 


PENCIL  MECHANICAL  DRAWING 


95 


4.  Eetrace  the  object  lines,   drawing:    (1)   horizontal  lines, 
beginning  at  the  top;   (2)  vertical  lines,  beginning  at  the  left; 
(3)   inclined  lines. 

5.  Draw  extension  and  dimension  lines  and  put  in  dimensions. 

6.  Letter  a  note,  giving  the  number  of  parts  required  and 
the  material  from  which  they  are  to  be  made. 

7.  Letter  the  title,  using  the  name  of  the  object  given  below 
the  figure  from  which  the  drawing  was  made. 


FIG.  95.     JOURNAL  BEARING  FOR  ELECTRIC  RAILWAY  MOTOR  CAR 
EIGHT  WANTED — BRASS 


PREPARATORY    INSTRUCTIONS   FOR   PLATE    16 

Tangencies.  In  either  freehand  or  mechanical  drawing 
where  a  straight  line  is  tangent  to  an  arc,  the  arc  should  be 
drawn  first.  In  the  constructive  stage  the  arc  should  be  drawn 
long  enough  so  that  it  will  extend  beyond  the  point  of  tangency. 
Fig.  97.  The  straight  line  may  then  be  drawn  tangent  to  the 
arc.  Before  finishing  the  drawing  the  unnecessary  part  of  the 
arc  is  erased. 

Radius  Dimensions.  The  dimension  forms  for  radius  dimen- 
sions are  shown  in  Fig.  98.  When  the  distance  between  the  arc 
and  its  center  is  great  enough  to  admit  the  figures  and  arrow- 
heads the  form  is  as  shown  in  Fig.  98.  Note  the  circle  about 


96 


MECHANICAL  DRAWING 


the  center  in  place  of  an  arrowhead.  This  circle  should  be  made 

freehand  and  about  Ty  in  diameter.  When  the  distance  between 

the  arc  and  its  center  is  short  the  center  is  not  indicated  as 
shown  by  J"  radius,  Fig.  99. 


FIG.   96.     TYPE  PROBLEM — PERSPECTIVE  OF  BRAKE  LEVER  BRACKET 


FIG.  97.     TYPE  PROBLEM— CONSTRUCTIVE  STAGE  OF  MECHANICAL  DRAWING 


98 


MECHANICAL  DRAWING 

DATA  FOR  PLATE  16 


Given:     Perspective  sketches,  Figs.  99,  100,  and  101. 
Required:     To  draw  an  orthographic  sketch  of  the  object 
shown   in   Fig.   99,   100,   or   101   with   dimensions,   as   assigned 


FIG.  99.     BRUSH  HOLDER  BRACKET  FOR  PRESSURE  TUNNEL  CABLE  REEL 
Two  WANTED — CAST  IRON 


FIG.  100.    HINGE  BRACKET  FOE  GEAR  CASING  OIL  COVER 
Two  WANTED — CAST  IRON 

by  the  instructor.     The  student  should  decide  what  views  are 
necessary  to  show  the  form  of  the  object. 

Instructions:  In  drawing  the  circles  and  arcs  sketch  in  the 
center  lines  and  lay  off  the  radii  on  each,  as  in  Plate  10, 


PENCIL  MECHANICAL  DRAWING  99 

PREPARATORY    INSTRUCTIONS    FOR   PLATE    17 

Given:     The  orthographic  sketch,  Plate  16. 
Required:     To   make   a   pencil   mechanical   drawing   from 
Plate  16. 


DRILL  4" 


FIG.  101.     CLUTCH  LEVER  BRACKET  FOR  VALVE  OPERATING  MECHANISM 
ONE  WANTED — CAST  IRON 


Instructions:  1.  Draw   the   border   line   and   enclosing   rec- 
tangle. 

2.  Locate  and  draw  two  center  lines  at  right  angles  to  each 
other  for  each  arc  or  circle. 

3.  Draw  the  arcs  of  indefinite  length  so  that  they  extend 
beyond  the  points  of  tangency. 


100  MECHANICAL  DRAWING 

4.  Draw  the  straight  lines  tangent  to  the  arcs. 

5.  When  the  constructive  stage  is  complete  retrace  the  lines 
in  the  following  order:    (1)    circles  and  arcs;    (2)    horizontal 
lines,   beginning  at  the   top   of  the  sheet;    (3)    vertical  lines, 
beginning  at  the  left  of  the  sheet;  (4)  inclined  lines. 

6.  The  center  lines  may  be  produced  and  used  as  extension 
lines  where  appropriate. 

7.  Letter  a  note,  giving  the  number  of  parts  required  and 
the  materials  from  which  they  are  to  be  made. 

8.  Letter  the  title. 

SUMMARY 

In  this  chapter  orthographic  sketching  has  been  continued. 
A  more  general  application  of  the  principles  of  orthographic 
drawing  has  been  made.  This  has  been  done  principally  by 
introducing  problems  requiring  three  views  from  perspective 
sketches.  It  has  been  the  chief  aim  of  this  chapter  to  give  con- 
siderable practice  with  some  of  the  common  instruments  and 
materials  used  in  making  mechanical  drawings  and  to  fix  a 
standard  of  technique.  The  student  should  now  be  able  to  make 
neat,  accurate  mechanical  drawings  of  simple  objects.  The 
technique  of  the  lettering,  arrowheads,  and  figures  should  be  of 
a  standard  comparable  with  that  secured  in  the  mechanical 
line  work. 

As  a  means  of  reviewing  Chapter  III  the  following  questions 
and  problems  are  given : 

REVIEW  QUESTIONS 

1.  (a)  What  determines  the  number  of  views  of  an  object? 
(b)  When  are  more  than  two  views  necessary? 

2.  Where  is  the  front  surface  of  an  object  represented  in  the 
side  view? 

3.  (a)   What  dimension  is  common  to  the  top  and  side  views  ? 
(b)  If  only  the  top  and  side  views  were  drawn  how  should  they 
be  related? 


PENCIL  MECHANICAL  DRAWING  101 

4.  (a)    Describe  the  position  of  the   T-square  for  drawing 
horizontal  lines,     (b)  How  is  it  held?    (c)  Illustrate  by  a  sketch 
the  position  of  the  pencil  in  ruling  a  line  along  the  T-square. 

5.  Describe  the  process  of  squaring  and  fastening  the  paper 
011  the  board  for  a  mechanical  drawing. 

6.  (a)  What  is  the  shape  of  the  ruling  point  of  the  pencil? 
(b)  How  is  it  obtained?     (c)  How  does  the  measuring  point  of 
the   mechanical   drawing   pencil   differ  from  the   point   of   the 
sketching  pencil  ? 

7.  (a)   Describe  the  positions  of  the  T-square  and  triangle 
for  drawing  a  vertical  line,     (b)   In  which  direction  is  the  line 
always  drawn  ? 

8.  (a)  What  is  the  shape  of  the  point  of  the  lead  used  in 
the  bow  compass?     (b)  How  should  it  be  set  with  reference  to 
the  needle  point? 

9.  Illustrate  by  a  sketch  and  show  calculations  for  deter- 
mining the  size  of  an  enclosing  rectangle. 

10.  Describe  the   process   of  drawing  the  border  rectangle 
for  a  mechanical  drawing  sheet. 

11.  (a)  Define    the    constructive   stage    of   the    mechanical 
drawing,     (b)   How  are  hidden  edges  shown  in  this  stage? 

12.  In  what  order  are  the  lines  drawn  in  the  finishing  stage  ? 

13.  (a)  What  space  is  left  between  the  outline  of  the  object 
and  the  end  of  the  extension  line?      (b)    How  far  should  the 
extension  line  run  beyond  the  arrowhead?     (c)  How  far  should 
the  nearest  dimension  line  be  from  the  outline  of  the  object? 
(d)  How  far  apart  should  dimension  lines  be  placed? 

14.  (a)  What  is  the  height  of  the  whole  number  in  a  dimen- 
sion?    (b)  The  total  height  of  the  fraction? 

15.  What  is  the  purpose  of  notes  on  a  drawing^ 

16.  What  information  does  the  title  contain? 

17.  What  is  the  title  block  ? 

18.  Describe  the  steps  taken  in  balancing  two  or  more  lines 
in  a  title. 

19.  What  dimension  forms  are  used  in  showing  the  inclina- 
tion of  a  line  ? 


102 


MECHANICAL  DRAWING 


20.  (a)  What  angles  can  be  obtained  with  each  triangle 
used  in  combination  with  the  T-square?  (b)  With  both  tri- 
angles used  in  combination  with  the  T-square? 


FIG.  102.     TOOL  HOLDER  FOR  24"  TURRET  LATHE — Six  WANTED — CAST  IRON- 


FIG  103.    BACK  REST  FOK  TURRET  LATHE — FOUR  WANTED — CAST  IRON 

21.  In  what  order  are  the  lines  drawn  when  an  arc  and  a 
straight  line  are  tangent  to  each  other? 

22.  (a)  Show  two  ways  of  dimensioning  a  radius,     (b)  Under 
what  condition  is  each  used  ? 


PENCIL  MECHANICAL  DRAWING  103 

DATA  FOE  EEVIEW  PROBLEMS 

Given:     A  perspective  sketch,  Fig.  102. 
Required : 

1.  To  make  an  orthographic  sketch  of  the  object  shown  in 
Fig.  102. 

2.  To  make  a  pencil  mechanical  drawing  from   the   ortho- 
graphic sketch. 


FIG.  104.     DASH  POT  ARM  FOR  22"x42"  CORLISS  ENGINE 
Two  WANTED — CAST  IRON 


Given :     A  perspective  sketch,  Fig.  103. 
Required : 

1.  To  make  an  orthographic  sketch  of  the  object  shown  i  i 
Fig.  103. 

2.  To  make  a  pencil  mechanical  drawing  from  the  ortho- 
graphic sketch. 

Given:     A  perspective  sketch,  Fig.  104. 
Required : 

1.  To  make  an  orthographic  sketch  of  the  object  shown  in 
Fig.  104. 

2.  To  make  a  pencil  mechanical   drawing  from   the   ortho- 
graphic sketch. 


CHAPTER  IV 

TRACING  AND  BLUEPRINTING 
PREPARATORY    INSTRUCTIONS   FOR   PLATE    18 

The  Half  Section.  As  explained  under  Instructions  for 
Plate  11,  a  drawing  may  often  be  made  much  clearer  by  repre- 
senting the  object  with  a  portion  removed.  An  object  is  fre- 


FIG.  105.     TYPE  PROBLEM — COVER  FOR  LIMIT  SWITCH  Box 


quently  imagined  cut  through  an  axis  of  symmetry  into  two 
similar  parts.  The  view  of  the  object  obtained  by  looking  in 
a  direction  at  right  angles  to  the  cut  surface  is  called  a  half 
section.  In  Fig.  106  the  areas  representing  the  cut  surface  are 
crosshatched,  as  in  the  case  of  the  quarter  section,  with  parallel 
lines  about  TV'  apart.  The  angle  of  the  lines  is  usually  45°. 

The  student  should  test  his  knowledge  of  the  orthographic 
principles  involved  in  making  half  section  views  by  answering 
the  following  questions.  See  Fig.  107. 

104 


106 


MECHANICAL  DRAWING 


1.  Where  is  the  surface  1,  6,  shown  in  the  side  view? 

2.  (a)   Does  the  rectangle  20,  21,  22,  23  in  the  side  view 
represent  an  opening  or  a  solid  part  of  the  object?     (b)  Why? 


A 

i 
1 

| 

20 

21 

23 

22 

J 

—  !e 

S^ 

B 

FIG.  107 

REVIEW  PROBLEM 


3.  Where   is   the  surface   7,   4  shown   in   the   side   and  top 
views  ? 

4.  Make  a  front  view  of  the  object  when  cut  on  AB. 

5.  (a)   Is  the  side  view  affected  by  the  section?     (b)   Top 
view? 

Each  tracing  in  this  chapter  will  be  preceded  by  a  pencil 
mechanical  drawing.  The  pencil  drawing  is  made  to  give .  the 
student  additional  practice  in  the  handling  of  the  instruments 
already  used,  to  introduce  the  use  of  new  instruments,  and  to 
provide  drawings  for  the  tracings. 

DATA  FOR  PLATE  18 

Given:     Orthographic  sketches,  Figs.  108,  109,  and  110. 
Required:     To  make  a  pencil  mechanical  drawing  of  the 
object   shown   in   Fig.    108,    109,    or    110,    as   assigned   by   the 


TRACING  AND  BLUEPRINTING 


107 


•2'-f 


2-li- 


v>^ 


RIGHT  SIDE 

FIG.  108.     MANHOLE  HEAD  FOR  CATSKILL  AQUEDUCT  CONDUIT 
TWENTY-SEVEN  WANTED — OAST  IRON 


-4i" 


* 


7^ 


.±'-1. L-l |. 


I9S 


fM 


TI^L _j  r_i j ]  mi. 

L*«L.  XJ  J  HiL  ^'-*- 


FIG.  109.    AIR  PUMP  BRACKET  FOR  ATLANTIC  TYPE  LOCOMOTIVE 
ONE  WANTED — CAST  IRON 


108 


MECHANICAL  DRAWING 


instructor.    The  views  given  and  required  may  be  obtained  from 
the  following  table : 

Given 

Fig.  108.     Top  and  right  side  views. 

Fig.  109.     Top,  right  side,  and  front  views. 

Fig.  110.     Top,  right  side,  and  front  views. 


Required 


Scale 


Top  and  front  half  section  views.  ")  Quarter  size 

Top,  left  side,  and  front  half  section  views.  [-Quarter  size 

Top,  right  side,  and  front  half  section  views.  J  Half  size 

1 


'8 

'g 

T 

t 

j 

I 

"-IN 

,t 

! 

!               11 

n 

McO 

+ 



*— 

rl-  —  *—  Ir 

<  2 

7" 
8  ~ 

FIG.  110.     TRUCK  SPRING  SEAT  FOR  ATLANTIC  TYPE  LOCOMOTIVE 
EIGHT  WANTED — CAST  IRON 

Instructions:   Proceed  as  for  the  mechanical  drawing  plates 
of  Chapter  III. 


TRACING  AND  BLUEPRINTING 


PREPARATOEY    INSTRUCTIONS    FOR   PLATE    19 


109 


The  following  is  a  list  of  the  instruments  and  materials 
needed  to  make  tracings  of  mechanical  drawings.  See  Chap- 
ter V  for  complete  description  of  each: 

1.  Tracing  cloth. 

2.  Black  waterproof  ink. 

3.  Ruling  pen. 

4.  Compass. 

5.  Bow  pen. 


FIG.  111.    RULING  A  HORIZONTAL  LINE 


Tracing  Cloth.  It  will  be  noticed  that  one  side  of  the  tracing 
cloth  has  a  glazed  surface  and  the  other  a  dull  surface.  Either 
side  may  be  used  under  conditions  described  in  Chapter  V. 
For  the  tracings  of  this  chapter  use  the  dull  side. 

The  cloth  is  fastened  to  the  board  with  the  same  thumb 
tacks  used  to  hold  the  paper.  In  order  to  avoid  shifting  the 
paper  the  cloth  should  be  spread  over  the  sheet  and  one  tack 
at  a  time  removed  and  inserted  through  the  cloth  into  the  hole 
from  which  it  came. 

To  prepare  the  cloth  so  that  it  will  take  ink  readily  dust 
the  surface  lightly  with  powdered  chalk.  Rub  thoroughly  and 
remove  all  superfluous  chalk. 

Black  Ink.  Black  ink  will  be  used  for  all  lines  on  the  plates 
of  this  chapter.  Replace  the  cork  in  the  bottle. 

The  Ruling  Pen  should  be  held  in  the  hand  as  shown  in 
Fig.  111.  Note  that  the  first  finger  rests  above  the  thumb  screw 
with  the  second  finger  against  the  right  side  of  the  pen.  The 


110  MECHANICAL  DRAWING 

pen  should  be  held  i*.  a  vertical  plane,  but  it  may  lean  slightly 
to  the  right.  In  this  position  both  nibs  will  touch  the  cloth 
with  equal  pressure,  which  is  essential  to  the  production  of 
smooth,  sharply  defined  lines.  Before  using  the  pen  it  should 
be  tested  as  described  in  Chapter  V.  The  pen  should  be  filled 
to  the  height  shown  in  Fig.  Ill,  about  J",  by  inserting  the  ink 
between  the  nibs  with  the  quill  which  is  attached  to  the  stopper 
of  the  bottle.  Care  should  be  taken  to  avoid  getting  ink  on  the 
outside  surfaces  of  the  nibs.  The  pen  should  be  adjusted  to 
approximately  the  width  of  line  required,  before  being  filled. 


FIG.  112.    DRAWING  A  CIRCLE  WITH  THE  COMPASS 

After  it  is  filled  it  may  be  adjusted  to  the  exact  width  of  line. 
Clean  the  pen  frequently  by  pulling  a  cloth  downward  between 
the  nibs. 

The  center  of  the  ink  line  should  be  directly  over  the  pencil 
line  in  tracing.  Care  must  be  taken  to  set  the  pen  exactly  at 
the  beginning  of  a  line.  At  the  end  of  a  line  the  pen  should 
be  lifted  vertically  in  order  that  the  ink  may  not  draw  out  and 
cause  the  line  to  overrun.  In  drawing  dotted  lines  the  pen 
must  be  set  down  vertically,  the  dash  drawn  and  the  pen  then 
lifted  vertically  so  as  to  make  both  ends  of  the  dash  square. 

The  spacing  of  section  lines  is  done  entirely  by  eye.  In 
order  to  avoid  varying  the  spaces  the  pen  should  be  placed 


TRACING  AND  BLUEPRINTING  111 

against  the  ruling  edge  and  the  distance  from  the  point  of  the 
pen  to  the  last  line  drawn  made  equal  to  the  perpendicular 
distance  between  any  two  sequential  preceding  lines. 

When  starting  the  crosshatching  in  a  corner  there  is  a  tend- 
ency to  space  the  lines  too  closely,  the  spaces  increasing  as  the 
lines  become  longer.  The  student  should  practice  crosshatching 
rectangular  areas  on  a  scrap  of  tracing  cloth  before  attempting 
the  work  on  the  drawing. 

The  Compass.  When  using  the  compass  for  either  penciling 
or  inking,  the  legs  should  be  adjusted  so  that  the  pen  or  pencil 
part  and  the  needle  point  are  perpendicular  to  the  drawing 
board.  With  the  legs  in  this  position  the  compass  revolves  about 
the  needle  point  as  an  axis  and  the  two  nibs  of  the  pen  bear 
with  equal  pressure,  thus  producing  sharply  defined  lines.  The 
compass  is  held  by  the  handle,  between  the  thumb  and  first  finger 
of  the  right  hand.  It  is  rotated  by  rolling  the  handle  between 
the  thumb  and  finger.  Fig.  112.  The  compass  should  be  filled, 
adjusted,  and  cared  for  in  the  same  manner  as  the  ruling  pen. 

The  Bow  Pen  is  used  for  all  circles  and  arcs  of  J"  radius  or 
less.  The  pen  should  be  filled  and  the  nibs  adjusted  in  the  same 
manner  as  the  ruling  pen. 

CENTEE    LINE ^ 

EXTENSION    LINE 

DIMENSION    LINE frh"  WIDE 

CEOSSHATCHING    LINEj 


BOEDEE  LINE •&"  WIDE 

FIG.  113.    LINE  NOTATION  FOR  INK  DRAWINGS 

Line  Notation.  In  inking,  the  object  lines  are  drawn  notice- 
ably heavier  than  all  other  lines  except  the  border  line.  The 
difference  in  width  thus  secured  produces  a  sharp  contrast 
between  classes  of  lines,  which  makes  the  drawing  easy  to  read 
and  gives  it  a  good  appearance.  In  small  drawings  or  those 
containing  intricate  detail  the  width  of  the  object  lines  is  slightly 
reduced.  In  this  course  the  standard  widths  of  lines  are  as 
follows.  See  Fig.  113  : 

1.  Object  lines  (full  and  dotted),  fa"  wide. 


112  MECHANICAL  DRAWING 

2.  Center,    extension,    dimension,    and    crosshatching    lines, 
T!S"  (estimated  one-half  the  width  of  the  object  lines). 

3.  Border  line,  -fa"  wide. 

Where  lines  of  the  same  width  are  to  be  made  with  two 
different  instruments,  sample  lines  should  be  drawn  on  a  scrap 
of  tracing  cloth  and  the  pens  adjusted  until  the  lines  are  of 
exactly  the  same  width. 

The  dotted  lines  should  be  composed  of  alternate  -J"  dashes 
and  fa"  spaces.  A  -fa"  space  should  also  be  left  between  the  end 
of  the  extension  line  and  the  outline  of  the  object.  Correct  and 
incorrect  methods  in  line  notation  are  shown  in  Fig.  56. 

Order  of  Inking  the  Drawing.  The  drawing  should  be  inked 
in  the  order  given  below  to  secure  economy  of  time  and  effort. 

1.  Object  lines. 

a.  Circles  and  arcs  of  circles. 

b.  Horizontal  lines  (beginning  at  the  top). 

c.  Vertical  lines  (beginning  at  the  left). 

d.  Inclined  lines. 

2.  Center  lines  (same  order  as  object  lines). 

3.  Extension   and    dimension   lines    (same    order   as    object 
lines). 

4.  Arrowheads. 

5.  Dimension  figures  and  notes. 

6.  Crosshatching  lines. 

7.  Title. 

8.  Border  line. 

In  inking  the  title  and  notes,  pencil  guide  lines  on  the  tracing 
cloth  will  be  found  of  great  assistance  in  keeping  the  letters 
uniform  in  height. 

Erasure.  When  it  is  found  necessary  to  erase  a  line  the 
shield  should  be  used  as  in  the  pencil  drawing.  A  ruby  pencil 
eraser  will  remove  the  ink  with  the  least  injury  to  the  cloth. 
The  line  can  then  be  re-inked  if  necessary  with  little  danger 
of  the  ink's  spreading.  When  a  blot  occurs  in  an  open  area  as 
much  of  the  wet  ink  should  be  removed  at  once  as  possible  and 
the  spot  allowed  to  dry  before  attempting  to  erase. 

Trimming  the  Tracing  Cloth.    When  the  tracing  is  finished 


TRACING  AND  BLUEPRINTING 


113 


lay  off  J"  from  each  corner  of  the  border  rectangle  to  make 
a  one-half  inch  margin.  Place  the  tracing  on  the  back  of  the 
drawing  board.  With  a  sharp  knife  running  along  the  edge 
of  the  T-square  blade  not  used  for  ruling,  trim  the  sheet 
to  the  rectangle  determined  by  the  eight  pencil  points.  The 
T-square  blade  should  be  placed  over  the  finished  sheet.  The 
drawing  will  then  be  held  firmly  and  will  be  protected  from  the 
knife  in  case  it  should  slip. 


FIG.    114.     TYPE   PROBLEM — CLUTCH   SHOE — GIVEN   VIEWS 

DATA  FOR  PLATE  19 

Given:     The  pencil  mechanical  drawing,  Plate  18. 
Required:     To  make  a  tracing  of  Plate  18. 
Instructions: 

1.  Fasten  the  tracing  cloth  over  the  mechanical  drawing  and 
prepare  the  surface  for  inking  as  previously  described. 

2.  Ink    the    drawing    following    the    steps    outlined    under, 
"Order  of  Inking  the  Drawing,"  page  112. 

3.  Trim  the  sheet  to  Il"xl5". 


TRACING  AND  BLUEPRINTING 


DATA  FOR  PLATE  20 


115 


Given:     Orthographic  sketches,  Figs.  116,  117,  and  118. 

Required:  To  make  a  pencil  mechanical  drawing  of  the 
object  shown  in  Fig.  116,  117,  or  118,  as  assigned  by  the  in- 
structor. The  views  given  and  required  may  be  obtained  from 
the  following  table: 


FIG.   116.    CLUTCH  BRACKET  FOR  PRESSURE   TUNNEL  HOISTING  CAGE 
Two  WANTED — CAST  IRON 

Given 

Fig.  116.     Top,  left  side,  and  front  views. 
Fig.  117.     Front  and  left  side  views. 
Fig.  118.     Front  and  right  side  views. 


116 


MECHANICAL  DRAWING 


Required  Scale 

Top,  front,  and  right  side  views.  1  Half  size 
Front  and  right  side  views.  iQuarter  size 


Front  and  left  side  views. 


Half  size 


H 


I 


I      'CO 


HOLES  TO  SUIT  MOTOR  USED 


20' 


LEFT  5IDEL 

FRONT 

FIG.  117.    MOTOR  BRACKET  FOR  VALVE  OPERATING  MECHANISM 
ONE  WANTED — CAST  IRON 


FIG.  118.     THROTTLE  LEVER  FULCRUM  FOR  ATLANTIC  TYPE  LOCOMOTIVE 
ONE  WANTED — CAST  IRON 

PREPARATORY    INSTRUCTIONS   FOR    PLATE    21 

Blueprints  should  be  made  from  the  following  tracings  in 
order  that  the  student  may  see  that  the  lines  on  his  tracing 
produce  lines  of  the  proper  width  on  the  blueprint. 


TRACING  AND  BLUEPRINTING  117 

Blueprinting.  The  most  common  method  of  reproducing 
drawings  is  by  blueprinting.  Blueprints  are  made  on  a  white 
paper,  one  side  of  which  has  been  coated  with  a  solution  sensi- 
tive to  light.  To  make  the  prints,  the  inked  side  of  the.  tracing 
is  placed  against  the  glass  of  a  printing  frame.  The  sensitized 
side  of  the  blueprint  paper  is  then  placed  against  the  tracing 
cloth  and  held  firmly  in  contact  with  it. 

The  length  of  exposure  to  the  light  depends  on  the  intensity 
of  the  sunlight  or  electric  light  and  upon  the  " speed"  of  the 
blueprint  paper.  After  removing  the  paper  from  the  frame 
it  should  be  washed  by  turning  it  over  several  times  in  a  basin 
of  water.  This  removes  the  chemical  on  the  sensitized  side  of 
the  paper  which  was  covered  by  the  lines  of  the  drawing  on  the 
tracing  cloth  and  leaves  the  white  paper  exposed,  forming  the 
outline  of  the  blueprint  drawing.  The  result  is  a  reproduction 
of  the  drawing  in  white  lines  with  a  blue  background. 


DATA  FOR  PLATE  21 

Given:     The  pencil  mechanical  drawing,  Plate  20. 
Required:    To  make  a  tracing  of  Plate  20. 

Instructions: 

1.  Fasten   the  tracing  cloth   over  the  mechanical   drawing 
and  prepare  the  surface  for  inking. 

2.  Ink   the    drawing,    following   the    steps   outlined   under, 
"Order  of  Inking  the  Drawing,"  page  112. 

3.  Trim  the  sheet  and  press  the  cloth  back  into  the  tack 
holes. 

PREPARATORY    INSTRUCTIONS   FOR   PLATE    22 

Tangencies.  In  mechanical  drawing  where  a  straight  line 
is  tangent  to  an  arc,  the  arc  should  be  drawn  first.  In  the 
constructive  stage  the  arc  should  be  drawn  long  so  that  it  will 
extend  beyond  the  point  of  tangency.  A  straight  edge  may 
then  be  laid  tangent  to  the  arc  and  the  straight  line  drawn  in. 


118 


MECHANICAL  DRAWING 


Before  the  drawing  is  finished  the  unnecessary  part  of  the  arc 
is  erased. 

Centers  for  rounded  corners,  fillets  and  other  arcs  of  circles, 
which  do  not  have  their  centers  on  any  line  of  the  drawing, 

v  .     v  \ 


FIG.   119.     "TRIAL  AND  ERROR"  METHOD  OF  LOCATING  CENTERS 

are  located  by  what  is  called  the  "trial  and  error"  method. 
The  compass  should  be  first  adjusted  to  the  proper  radius. 
To  locate  the  center  of  the  arc,  set  the  lead  on  the  tangent  line 
at  A,  Fig.  119,  estimating  A  C  as  nearly  as  possible  equal  to 


RElAMg 


=f- 


u* 


kf 


I 


1  * 

-1.P 


LEFT  SIDE 

FRONT 

FIG.   120.     TYPE   PROBLEM — IGNITOR  BODY — GIVEN  VIEWS 


the  radius  of  the  arc.  Set  the  needle  point  at  B  opposite  A  and 
bring  the  lead  around  to  D.  Move  the  needle  point  parallel  to 
A  C  an  amount  equal  to  the  error.  Then  the  compass  should 
be  again  rotated  back  to  A  to  test  for  accuracy,  and  if  necessary 
further  adjustment  should  be  made  before  drawing  the  arc. 


120 


MECHANICAL  DRAWING 

DATA  FOR  PLATE  22 


Given:     Orthographic  sketches,  Figs.  122,  123,  and  124. 
Required:     To  draw  the  views  of  the  object  shown  in  Fig. 
122,  123,  or  124,  as  assigned  by  the  instructor.    See  table  below. 


TOP 


RIGHT   SIDE 

FIG.  122.    STUFFING  Box  GLAND  FOR  22"x42"  CORLISS  ENGINE 
ONE  WANTED — CAST  IRON 


TOP 


RIGHT   SIDE 

FIG.   123.     BEARING  FOR  2%"   SHAFT — ONE  WANTED — CAST  IRON 


Given 

Fig.  122.  Top  and  right  side  views. 
Fig.  123.  Top  and  right  side  views. 
Fig.  124.  Top  and  right  side  views. 


TRACING  AND  BLUEPRINTING 
Required  Scale 

Top  and  front  half  section  views.  "1  Full  size 
Top  and  front  half  section  views.  >Full  size 
Top  and  front  half  section  views.  J  Half  size 


121 


RIGHT  5IDE 

FIG.  124.     STUFFING  Box  FOR  36"  GATE  VALVE — ONE  WANTED — CAST  IRON 


PREPARATORY   INSTRUCTIONS   FOR   PLATE    23 

Locating  Points  of  Tangency.  To  secure  perfect  joints 
where  lines  are  tangent  in  the  tracings  the  exact  points  of  tan- 
gency  should  be  located  and  marked  in  pencil  on  the  tracing 
cloth.  The  method  of  locating  the  tangent  points  depends  upon 
the  geometrical  principle,  that  a  .line  perpendicular  to  a  tan- 
gent at  its  point  of  contact  passes  through  the  center  of  the 
circle. 

To  locate  a  point  of  tangency  place  the  hypotenuse  of  either 
triangle  against  any  edge  of  the  other  triangle,  as  shown  in 
Fig.  125.  Move  them  as  one  tool  until  a  side  of  the  triangle  A 
is  coincident  with  the  tangent  line.  With  triangle  B  held 
firmly  in  place,  slide  triangle  A  into  the  position  marked  A' 
where  the  side  at  right  angles  to  the  tangent  line  passes  through 


122  MECHANICAL  DRAWING 

the  center  of  the  arc.  A  short  dash  should  be  drawn  across  the 
tangent  line  to  mark  the  point  of  tangency. 

The  -point  of  tangency  between  two  arcs  may  be  located  by 
drawing  the  straight  line  joining  their  centers.  This  line  passes 
through  their  point  of  contact. 


FIG.  125.     METHOD  OF  LOCATING  POINTS  OF  TANGEXCY 
DATA  FOR  PLATE  23 

Given:     The  pencil  mechanical  drawing,  Plate  22. 
Required:     To  make  a  tracing  from  Plate  22. 

Instructions: 

1.  Fasten  the  tracing  cloth  and  prepare  it  for  inking. 

2.  Locate  the  points  of  tangency. 

3.  Ink  the  drawing  in  the. usual  order. 

4.  Trim  the  sheet  and  press  the  cloth  back  into  the  tack  holes. 

SUMMARY 

The  pencil  mechanical  drawing  of  Chapter  III  has  been  con- 
tinued in  this  chapter  to  develop  further  skill  in  the  use  of 
instruments  and  to  improve  the  technique  in  both  the  mechanical 
and  freehand  elements  of  the  drawing.  It  has  been  the  chief 


TRACING  AND  BLUEPRINTING  123 

aim  of  this  chapter  to  familiarize  the  student  with  the  instru- 
ments, materials,  and  methods  used  and  to  fix  a  standard  of 
technique  in  inking.  The  student  should  now  be  able  to  make 
neat  tracings  with  proper  width  of  lines,  good  joints,  and 
uniform  spacing  in  crosshatching.  The  technique  of  the  letter- 
ing, arrowheads,  and  figures  should  be  comparable  with  that 
secured  in  the  mechanical  line  work. 

REVIEW  QUESTIONS 

1.  (a)    Define  half  section,      (b)    How  does  a  half  section 
differ  from  a  quarter  section  ? 

2.  (a)  What  is  the  difference  between  the  two  sides  of  the 
tracing  cloth?     (b)  Which  side  is  used  in  this  course? 

3.  (a)  Describe  the  process  of  fastening  the  cloth  over  the 
pencil  drawing,     (b)  How  is  the  cloth  prepared  for  inking? 

4.  (a)  How  is  the  ruling  pen  held  for  ruling  lines  ?     (b)  How 
is  it  adjusted  to  the  proper  width  of  line?     (c)  How  is  it  filled? 
(d)  How  cleaned? 

5.  (a)  What  precautions  are  taken  in  beginning  and  ending 
a  line?     (b)   How  does  the  pen  approach  and  leave  the  paper 
in  drawing  dotted  lines? 

6.  How  are  the  spaces  between  crosshatching  lines  estimated  ? 

7.  (a)   Why  are  the  needle  point  and  the  pen  and  pencil 
points  of  the  compass  set  at  right  angles  to  the  plane  of  the 
drawing  paper?     (b)   How  is  the  compass  held  when  drawing  a 
circle?     (c)   How  is  it  rotated? 

8.  (a)   In  inking  why  are  the  object  lines  made  wider  than 
the  other  lines?     (b)   Give  the  standard  width  of  inked  object, 
extension,  dimension,  and  center  lines,  and  the  border  line. 

9.  In  what  order  are  the  different  kinds  of  lines  inked  ? 

10.  (a)  In  what  order  are  the  object  lines  inked?     (b)  Cen- 
ter lines?     (c)  Extension  and  dimension  lines? 

11.  How  is  ink  removed  from  a  drawing? 

12.  How  is  the  tracing  trimmed  to  the  required  size? 

13.  (a)   Upon  what  geometrical  principle  does  the  method 
of  finding  the  point  of  tangency  between  an  arc  and  a  straight 
line  depend?     (b)  Give  the  steps  in  the  construction  necessary 
to  locate  a  point  of  tangency. 


124" 


MECHANICAL  DRAWING 
DATA  FOR  REVIEW  PROBLEMS 


Given:     The  top,  front,  and  right  side  views  of  an  object. 
Fig.  126. 

Required:     To  draw  the  top,  front  half  section,  and  right 
side  views  of  the  object  shown  in  Fig.  126.     Scale,  full  size. 


FIG    126.     SAND  Box  BRACKET  FOR  ATLANTIC  TYPE  LOCOMOTIVE 
ONE  WANTED — CAST  IRON 


Given:     The  top,  front,  and  right  side  views  of  an  object. 
Fig.  127. 

Required:     To  draw  the  top,  front,  and  left  side  views  of 
the  object  shown  in  Fig.  127.     Scale,  half  size. 

Given :     The  top  and  right  side  views  of  an  object.    Fig.  128. 

Required :     To  draw  the  top  and  front  half  section  views  of 
the  object  shown  in  Fig.  128.    Scale,  half  size. 


TORI  i 


Fie.  127.     DEAD  LEVER  FULCRUM  FOR  ATLANTIC  TYPE  LOCOMOTIVE 
ONE  WANTED — CAST  IRON 


FIG.  128.     STUFFING  Box  GLAND  FOR  36"  GATE  VALVE 

ONE  WANTED — CAST  IRON  (125) 


CHAPTER  V 

INSTRUMENTS  AND  MATERIALS 

Drawing  Paper.  In  selecting  a  drawing  paper  the  drafts- 
man should  have  in  mind  the  purpose  for  which  it  is  to  be  used. 
The  quality  of  the  paper  required  depends  upon  such  elements 
as  the  following:  The  nature  of  the  drawing,  whether  freehand 
or  mechanical ;  whether  it  is  to  be  a  rough  sketch  or  a  fine  line 
drawing;  whether  or  not  the  drawing  is  to  be  inked;  the 
amount  of  erasing  necessary,  etc.  For  whatever  purpose  it  is 
to  be  used  the  paper  should  be  strong  and  have  a  uniform 
surface  and  thickness. 

For  freehand  drawing,  where  it  is  desired  to  produce  a 
porous,  uniform  line  with  a  soft  pencil,  a  slightly  grained  sur- 
face is  satisfactory.  It  should  stand  erasing  without  injury. 
These  qualities  are  essential  for  the  paper  used  in  the  per- 
spective and  orthographic  sketching  in  this  course. 

Under  some  conditions  in  orthographic  sketching  it  is  con- 
venient to  use  cross-section  paper.  Fig.  276.  By  its  use  the 
views  of  a  complicated  object  are  more  easily  related  and  their 
details  are  more  readily  proportioned.  It  will  be  found  of  special 
value  in  sketching  the  machine  parts  described  in  Chapter  VIII. 

For  mechanical  drawing,  where  a  sharp,  fine  line  is  to  be 
produced  with  a  hard  pencil,  a  tough,  hard  paper  should  be 
used.  It  should  stand  considerable  erasing  without  injury  to 
the  surface.  It  should  not  become  brittle  or  discolored  from 
reasonable  exposure  or  age.  If  freehand  lettering  is  to  be  done 
the  surface  must  be  reasonably  smooth  to  secure  the  best  results. 
If  considerable  time  is  to  be  spent  on-  a  drawing,  a  paper  should 
be  selected  which  has  an  agreeable  tint  and  which  will  not  soil 
easily  with  handling.  The  paper  used  for  the  mechanical  draw- 
ings of  this  course  must  fulfil  these  requirements. 

126 


INSTRUMENTS  AND  MATERIALS  127 

The  more  common  brands  of  drawing  paper  may  be  pur- 
chased either  in  sheets  or  rolls.  The  standard  names  and  sizes 
of  sheets  are  as  follows : 

Cap : .   13"xl7"  Imperial 22"x30" 

Demy   15"  x20"  Atlas 26"  x34" 

Medium    17"x22"  Double  Elephant  ..  27"x40" 

Royal    19"  x  24"  Antiquarian 31"  x  53" 

Super  Royal   19"x27" 

In  rolls  the  same  brand  of  paper  is  usually  less  expensive 
than  in  sheets.  Rolls  vary  in  width  from  twenty-seven  to 
seventy-two  inches.  Small  rolls  are  sold  by  the  linear  yard  and 
large  rolls  by  weight. 

Tracing  Paper.  For  temporary  drawings,  especially  where 
some  part  of  a  machine  or  structure  is  to  be  duplicated,  a  thin 
transparent  paper  called  tracing  paper  may  be  used  with  a 
considerable  saving  of  time.  It  should  not  be  used  for  a  perma- 
nent drawing  or  one  which  will  require  much  handling. 

Tracing  Cloth  is  a  thin,  firm  cloth  sized  to  hold  ink  and  to 
make  the  cloth  transparent,  It  is  generally  used  when  draw- 
ings are  to  be  reproduced  by  the  blue,  black,  or  brown  printing 
process.  Drawings  made  on  tracing  cloth  may  be  kept  indefi- 
nitely if  the  cloth  is  kept  dry  and  handled  carefully.  The 
drawings  may  be  changed  and  new  prints  made  from  time  to 
time. 

One  side  of  the  cloth  is  glazed  and  the  other  is  dull.  Either 
side  may  be  used  for  inking.  The  glazed  side  will  admit  of 
more  erasing,  but  when  inking  is  done  on  this  side  the  cloth  will 
curl.  For  work  where  penciling  is  to  be  done  on  the  cloth, 
for  drawings  to  be  used  for  photographic  reproduction,  and  for 
tinting,  the  dull  side  should  be  used. 

Sometimes  the  ink  does  not  adhere  to  the  surface  of  the 
cloth,  particularly  when  the  glazed  side  is  used.  To  overcome 
this  difficulty  powdered  chalk  may  be  rubbed  into  the  surface 
with  a  soft  cloth.  The  chalk  should  be  thoroughly  removed 
before  inking. 

Blueprint  Paper.  Instead  of  sending  the  tracing  into  the 
shop  where  it  would  soon  be  injured  or  worn  out,  prints  are 


128 


MECHANICAL  DRAWING 


made,  usually  on  blueprint. paper.  This  is  a  white  paper  covered 
with  a  solution  which,  after  being  exposed  to  light,  turns  blue 
when  washed  in  water.  The  result  is  white  lines  on  a  blue 
background.  The  method  of  making  blueprints  is  described  in 
detail  on  page  117. 

Van  Dyke  Paper  is  similar  to  blueprint  paper  except  that 
it  gives  a  white  line  on  a  brown  background.     It  is  usually  used 


T 


CORRECT  AVOID 

FIG.  129.    POSITION  OF  THUMB  TACKS 


for  making  negatives  from  which  positive  blueprints  are  made — 
i.  e.,  prints  having  blue  lines  on  a  white  background. 

Thumb  Tacks.  Drawing  paper  and  tracing  cloth  are  fast- 
ened to  the  drawing  board  by  means  of  thumb  tacks.  In  order 
that  the  thumb  tacks  may  hold  the  paper  or  cloth  firmly  and 
not  be  an  obstruction  to  the  T-square  and  triangles,  they  should 
be  pressed  down  vertically  until  the  heads  are  flush  with  the 
paper.  Fig.  129. 

Pencils.  The  lead  of  the  drawing  pencil  should  be  of  firm, 
even  grain.  To  secure  the  desired  effect  in  the  drawing  the 


INSTRUMENTS  AND  MATERIALS  129 

hardness  of  the  pencil  must  be  considered  in  connection  with 
the  surface  of  the  paper.  For  freehand  drawing  a  soft  pencil 
should  be  used  on  a  slightly  grained  surface.  A  soft  pencil 
is  easily  controlled  and  consequently  there  is  more  freedom  in 
drawing  lines  with  it  than  can  be  secured  with  a  hard  pencil.  The 
soft  sketching  pencil  should  be  sharpened  to  a  blunt  conical 
point,  as  described  on  page  18. 

For  mechanical  drawing,  where  it  is  desired  to  produce  fine 
sharp  lines,  a  hard  pencil  should  be  used  on  a  comparatively 
smooth,  hard  surfaced  paper.  One  end  of  the  mechanical  draw- 
ing pencil  should  be  sharpened  to  a  wedge  point  for  ruling  full 
lines  and  the  other  end  to  a  fine  conical  point  for  laying  off 
measurements  and  making  dotted  lines.  The  method  of  sharp- 
ening the  pencil  is  described  on  page  84. 

Drawing  pencils  are  graded  as  to  hardness  as  follows : 

Soft :  6B,  5B,  4B,  3B,  BB,  B. 
Medium :  F,  H,  HH,  3H,  4H. 
Hard :  5H,  6H,  7H,  8H,  9H. 

Manipulation  of  the  Pencil.  In  sketching,  the  pencil  is  held 
as  in  writing.  Horizontal  lines  are  drawn  in  short  sections  with 
a  wrist  movement.  The  hand  is  moved  into  a  new  position  for 
each  section.  In  drawing  vertical  lines  the  strokes  are  made 
downward  with  a  finger  movement.  See  page  20. 

For  the  short  strokes  in  lettering  the  finger  movement  is 
used  since  the  muscles  of  the  fingers  are  more  sensitive  than 
those  of  the  wrist  or  arm.  The  vertical  strokes  are  made  with 
a  finger  movement  and  the  horizontal,  inclined,  and  curved 
strokes  with  a  combined  finger  and  wrist  movement. 

In  ruling  lines  the  pencil  is  inclined  slightly  forward  and  the 
line  is  drawn  with  a  movement  of  the  hand  and  forearm.  See 
page  85. 

The  Eraser.  Ordinarily  a  medium  hard  eraser,  such  as  the 
ruby,  is  used  for  removing  pencil  lines  from  a  drawing.  A 
soft  flexible  eraser  is  very  satisfactory  for  cleaning  a  pencil 
drawing  without  erasing  the  lines.  When  erasing  lines  the 
paper  near  the  lines  to  be  erased  should  be  held  down  with  the 
thumb  and  first  finger  of  the  left  hand  to  prevent  it  from  crum- 


130  -  MECHANICAL  DRAWING 

bling  or  tearing.  On  ink  drawings  erasures  must  be  carefully 
made,  especially  if  inking  is  to  be  done  over  the  erased  areas. 
It  will  be  found  that  if  the  ruby  eraser  is  used  for  removing 
ink  lines  the  drawing  surface  will  be  left  in  good  condition  for 
re-inking.  In  case  a  blot  occurs  the  ink  should  not  be  allowed 
to  soak  into  the  tracing  cloth.  As  much  of  the  ink  as  possible 
should  be  taken  up  with  a  blotter  or  cloth  and  the  remainder 
allowed  to  dry  before  erasing. 

The  Erasing  Shield  is  used  to  protect  the  parts  of  the  draw- 
ing which  are  not  to  be  erased.  The  opening  best  suited  to 
expose  only  the  part  to  be  erased  is  selected  The  shield  is  held 


FIG.  13O    USING  THE  ERASER  AND  SHIELD 

in  position  on  the  drawing  with  the  thumb  and  first  finger  of 
the  left  hand,  while  the  eraser  is  applied  with  the  right.  Fig. 
130.  Where  the  openings  are  not  of  a  suitable  form  a  shield 
may  be  made  by  cutting  a  hole  in  a  piece  of  celluloid  or  thin 
stiff  paper.  Stock  erasing  shields  are  made  of  brass  or  celluloid. 
The  Drawing  Board  should  be  made  of  well  seasoned, 
straight  grained,  soft  wood,  free  from  knots  and  cracks.  The 
best  boards  are  designed  to  prevent  warping,  various  means 
being  used  to  accomplish  this  end.  Some  are  built  up  of  narrow 
strips  gluod  together;  others  have  a  series  of  saw  cuts  in  the 
back  running  lengthwise  with  the  grain  to  reduce  the  transverse 
strength  Such  boards  are  made  rigid  by  cleats  of  hard  wood 
screwed  through  oblong  slots  fitted  with  metal  bushings  to  the 


INSTRUMENTS  AND  MATERIALS 


t 


131 


back  of  the  board.  This  construction  allows  the  board  to  expand 
and  contract,  the  screws  sliding  in  the  slots.  The  board  is  also 
equipped  with  side  ledges  or  strips  of  hardwood  set  into  the 
end  edges  to  allow  the  T-square  to  move  easily.  Fig.  131. 

For  accurate  work  it  is  necessary  that  the  edge  of  the  board, 
against  which  the  head  of  the  T-square  is  placed,  be  perfectly 
straight  and  that  the  face  of  the  board  be  a  perfect  plane.  To 
test  the  edges  of  the  board  place  on  each  a  standard  straight 


FIG.  131.     DRAWING  BOARDS 


edge  or  the  edge  of  a  T-square  blade  which  is  known  to  be 
straight.  An  edge  of  the  board  is  straight  if,  when  held  up  to 
the  light,  the  straight  edge  is  in  contact  at  all  points. 

The  surface  of  the  board  may  be  tested  in  like  manner  by 
placing  the  straight  edge  upon  it  in  various  positions. 

The  edges  and  surface  of  the  board  should  be  kept  free 
from  cuts,  scratches,  and  bruises.  The  board  should  not  be 
subjected  to  extremes  of  temperature  or  moisture. 

The  T-Square  is  used  to  draw  horizontal  lines  and  to  pro- 
vide an  edge  against  which  the  triangles  are  placed.  It  consists 


132  MECHANICAL  DRAWING 

of  a  rule  called  the  blade  attached  to  one  end,  which  is  a  cross- 
piece  called  the  head.  Fig.  132.  The  head  is  sometimes  fastened 
to  the  blade  by  means  of  a  swivel,  so  that  the  blade  may  be  set 
at  any  desired  angle. 

T-squares  are  made  of  steel,  hard  rubber,  and  wood.  The 
steel  blade  is  the  most  accurate  but  tends  to  soil  the  drawing. 
For  ordinary  work  wooden  blades  are  used.  They  are  usually 
made  of  maple,  mahogany,  or  pear  wood  and  their  edges  are 
often  lined  with  hardwood  or  celluloid, 

The  celluloid  edges  make  it  possible  to  see  lines  near  the 
one  to  be  drawn  and  are  therefore  quite  convenient  when  join- 
ing lines  at  corners,  etc. 


FIG.  132.    T-SQUARE — PLAIN  AND  SWIVEL  HEAD 

The  upper  or  working  edge  of  the  T-square  and  the  edge  of 
the  head  which  rests  against  the  drawing  should  be  perfectly 
straight.  The  edge  of  the  blade  may  be  tested  as  follows: 
(1)  Draw  a  long  line  along  the  edge  of  the  blade.  (2)  Reverse 
the  ends  of  the  blade  with  respect  to  the  ruled  line,  keeping 
the  same  side  up  and  bringing  the  same  edge  against  the  ruled 
line.  (3)  Draw  a  second  line  along  this  edge  of  the  blade.  If 
the  edge  of  the  blade  is  straight  the  two  lines  will  coincide. 
Both  the  head  and  the  blade  of  the  T-square  may  also  be  tested 
by  means  of  a  straight  edge.  Since  the  T-square  is  used  only 
for  ruling  parallel  lines,  and  as  lines  at  other  angles  are  drawn 
with  the  triangles  in  combination  with  the  T-square,  it  is  evi- 
dent that  the  edge  of  the  head  and  blade  need  not  be  exactly 
at  an  angle  of  90°  to  each  other. 


INSTRUMENTS  AND  MATERIALS 


133 


Care  should  be  taken  to  preserve  the  upper  edge  of  the 
blade  of  the  T-square  from  injury.  It  should  never  be  used 
as  a  guide  for  the  knife  in  cutting  paper. 

When  using  the  T-square  the  head  is  pressed  firmly  against 
the  edge  of  the  board  with  the  left  hand  as  shown  in  Fig.  86.  The 
lines  are  always  drawn  along  its  upper  edge. 

The  Triangles  are  used  in  combination  with  the  T-square 
for  drawing  lines  at  certain  angles  to  the  horizontal.  They  are 
used  in  combination  with  the  T-square  for  drawing  lines  at 
various  angles  with  lines  which  are  not  horizontal. 


o 


FIG.  133.     TESTING  THE  90°  ANGLE 


They  are  made  of  steel,  wood,  hard  rubber,  or  celluloid. 
Steel  triangles  are  used  for  the  most  accurate  work.  Triangles 
made  of  wood  are  easily  injured  and  are  likely  to  change  their 
shape.  Those  made  of  celluloid  have  the  advantage  of  being 
transparent  and  are  most  generally  used. 

For  accurate  work  it  is  necessary  that  the  edges  of  the  tri- 
angles be  straight  and  that  the  angles  be  true.  The  edges  may 
be  tested  by  the  method  given  for  testing  the  T-square. 

Assuming  that  the  edge  of  the  T-square  has  been  found  to 
be  straight,  the  90°  angle  of  a  triangle  may  be  tested  as  follows : 
Place  the  triangle  in  position  D,  as  shown  in  Fig.  133,  and 


134 


MECHANICAL  DRAWING 


draw  the  line  A  B.  If,  when  the  triangle  is  turned  over  into 
position  C,  the  vertical  edge  coincides  with  the  line  A  B,  the 
angle  is  90°.  When  the  90°  angle  of  the  45°  triangle  has  been 
found  true,  the  45°  angles  are  true  if  equal. 

Compare  the  two  45°  angles  as  follows,  Fig.  134:  (1)  Place 
the  triangle  against  the  T-square  and  draw  a  45°  line.  (2)  Turn 
the  triangle  over  so  that  the  other  45°  angle  conies  into  the 
position  previously  occupied  by  the  first.  If  the  edge  of  the 
triangle  coincides  with  the  line  drawn,  the  45°  angles  are  equal. 


o     o 

o 


o 


FIG.  134. 
TESTING  THE  45°  ANGLE 


FIG.  135. 
TESTING  THE  30°   AND  60°   ANGLES 


The  60°  angle  of  a  30°-60°  triangle  may  be  tested  as  follows : 

(1)  Draw  a  horizontal  line,  A  B,  along  the  T-square.     Fig.  135. 

(2)  Draw  a  60°  line,  B  C,  along  the  edge  of  the  triangle  crossing 
the  horizontal  line.     (3)   Turn  the  triangle  over  and  draw  a 
second  60°  line,  A  C,  completing  a  triangle.     If  the  triangle 
formed  is  equilateral  the  60°  angle  is  true. 

The  lengths  of  the  sides  of  the  triangle  may  be  compared  by 
means  of  the  dividers.  When  the  edges  are  straight  and  the 
90°  and  60°  angles  are  found  to  be  true,  the  remaining  angle, 
30°,  will  also  be  true. 


INSTRUMENTS  AND  MATERIALS 


135 


With  the  30°-60°  triangle,  lines  may  be  drawn  at  90°  to  the 
horizontal  and  at  30°  or  60°  with  the  horizontal  to  the  right  and 
to  the  left.  Fig.  136. 

With  the  45°  triangle,  lines  may  be  drawn  at  90°  to  the  hori- 
zontal and  at  45°  with  the  horizontal  to  the  right  and  to  the 
left.  Fig.  137. 

By  combining  the  two  triangles,  lines  may  be  drawn  at  15° 
or  75°  with  the  horizontal  to  the  right  and  to  the  left.  Fig.  138. 


o     o 
o     o 


o 


FIG.  156.     LINES  DRAWN  WITH 
THE  30° -60°  TRIANGLE 


FIG.  137.     LINES  DRAWN  WITH 
THE  45°  TRIANGLE 


Lines  parallel  to  any  given  line  may  be  drawn  by  placing 
the  two  triangles  in  contact  and  sliding  them  as  one  tool  until 
an  edge  of  one  of  them  coincides  with  the  given  line.  Fig.  139. 
With  the  triangle  A  held  firmly  in  place,  triangle  B  may  be 
moved  along  it  and  lines  drawn  parallel  to  the  given  line. 

Lines  perpendicular  to  the  given  line  may  be  drawn  along 
the  edge  of  triangle  B,  which  is  at  90°  to  the  given  line. 

The  direction  in  which  the  lines  should  be  drawn  along  the 
triangles  is  shown  in  Figs.  136  and  137.  The  forearm  should 
always  make  a  right  angle  with  the  line  being  drawn. 

The  edges  of  the  triangles  should  not  be  cut  or  bruised.  If 
they  are  allowed  to  fall  on  the  floor  a  corner  may  be  blunted  and 


136 


MECHANICAL  DRAWING 


as  a  result  the  angle  will  not  be  true.  The  celluloid  triangles 
should  not  be  allowed  to  remain  bent  for  any  length  of  time,  as 
they  will  remain  permanently  so. 


FIG.  138.    LINES  DRAWN  WITH  A  COMBINATION  OF  THE  30°-60°  AND  45° 

TRIANGLES 

The  Irregular  Curve  is  used  for  drawing  a  smooth  curve 
through  a  series  of  points.  It  is  made  from  the  same  materials 
as  the  triangles.  Various  sizes  and  forms  may  be  had  to  fit 
different  curves. 


v 
FIG.  139.    LINES  DRAWN  PARALLEL  OR  PERPENDICULAR  TO  ANY  GIVEN  LINE 


The  line  is  drawn  in  sections  obtained  by  selecting  portions 
of  the  irregular  curve  which  will  pass  through  a  number  of 
given  points.  Fig.  259.  It  is  seldom  advisable  to  draw  through 


INSTRUMENTS  AND  MATERIALS  137 

all  of  the  points  of  the  section  of  the  line  to  which  the  curve  is 
fitted,  since  the  direction  of  the  line  at  the  end  of  the  section 
is  apt  to  be  such  that  the  succeeding  section  cannot  be  joined 
to  it  to  produce  a  smooth  curve.  To  make  sure  of  a  good  joint 
the  curve  for  each  section  should  fit  back  a  short  distance  on 
the  preceding  section. 

Scales  are  used  for  taking  measurements  and  laying  off  dis- 
tances. They  are  made  of  paper,  steel,  and  wood.  Ordinarily 
scales  are  made  of  boxwood.  There  are  two  general  forms,  the 
flat  and  the  triangular.  The  flat  scale  may  have  from  one  to 
four  graduated  faces  and  the  triangular  scale  from  four  to  six 
graduated  faces.  The  graduations  are  placed  directly  on  the 
wooden  face  of  the  scale  or  the  face  is  coated  with  a  white 
compound  which  makes  the  graduations  easier  to  read. 


20 


FIG.  140.    BEADING  THE  ARCHITECT'S  SCALE 

The  faces  of  the  scales  are  graduated  as  follows : 

The  Engineer's  Scale  is  divided  to  10,  20,  30,  40,  50,  and  60 
parts  to  the  inch.  It  is  full  divided,  i.e.,  the  small  divisions 
are  marked  off  for  the  full  length  of  a  face. 

The  Architect's  Scale  is  divided  to  3\,  i3G,  i,  i,  f,  -J,  J,  1,  1J 
and  3  inches  to  the  foot.  The  edges  on  this  scale  are  open 
divided,  i.  e.}  only  the  portion  of  a  face  representing  one  foot  is 
subdivided  to  read  in  smaller  units.  One  face  of  the  scale  is 
usually  divided  to  TV'  ^or  its  full  length. 

To  illustrate  the  reading  of  the  architect's  scale  consider 
the  edge  designated  by  a  figure  1  at  the  end.  Fig.  140.  This 
indicates  that  one  inch  on  this  scale  represents  one  foot.  The 
inch  to  the  right  of  the  0  at  the  right  end  of  the  scale  is  divided 
into  forty-eight  equal  parts  so  that  each  of  the  smaller  divi- 
sions represents  J"  and  the  spaces  between  the  0,  3,  6  and 
9  represent  3"  each.  To  the  left  of  the  0  the  readings  1,  2,  etc., 
are  inches  and  therefore  represent  feet.  To  measure  off  2',  4^" 


138  MECHANICAL  DRAWING 

to  the  right  of  point  X,  place  the  2  opposite  the  point  and  read 
four  and  one-half  inches  to  the  right  past  the  0.  In  case  it  is 
desired  to  lay  off  this  distance  to  the  left  of  Y,  place  the  four  and 
one-half  inch  mark  opposite  Y  and  read  past  the  0  to  the  2. 

The  Proportional  Inch  Scale  is  divided  to  read  one-half  or 
one-fourth  inch  to  the  inch  and  has  one  face  divided  to  -fa"  for 
its  full  length.  The  open  divided  edges  are  read  in  the  same 
manner  as  is  the  architect's  scale.  The  difference  is  that  in  this 
case  the  large  division  represents  inches  instead  of  feet.  One  of 
the  large  divisions  is  subdivided  to  read  sixteenths. 

Drawing  Instruments.  In  beginning  drawing  it  is  important 
that  the  student  have  a  good  set  of  instruments.  It  is  difficult 
to  define  a  "good"  set  of  instruments,  for  the  better  grades 
are  extensively  imitated.  The  student  should  be  guided  in  his 
selection  either  by  some  experienced  draftsman  or  by  the  trade 
mark  and  the  price  charged  by  a  reliable  dealer. 

A  good  set  of  instruments  differs  from  a  poor  one,  mainly, 
in  the  quality  of  materials  used,  correct  tempering,  and  good 
workmanship.  The  steel  of  the  pens  must  be  properly  tempered 
so  that  when  once  sharpened  the  points  will  remain  in  good 
condition  for  a  reasonable  time.  The  compass  and  dividers 
must  be  so  made  that  they  will  retain  their  alignment  and  adjust- 
ment when  handled  with  ordinary  care.  These  qualities  can 
only  be  definitely  determined  after  the  instruments  have  been 
given  a  fair  trial. 

To  secure  uniformly  satisfactory  results  in  drawing  it  is 
necessary  to  start  with  a  good  set  of  instruments  and  to  keep 
them  in  good  condition.  In  the  following  discussion  the  selec- 
tion, use,  and  care  of  each  of  the  drawing  instruments  is 
considered. 

The  Compass  is  used  for  drawing  circles  and  arcs  of  circles. 
Fig.  112.  The  better  grades  are  made  of  German  silver.  It  is 
important  that  a  compass  be  light,  yet  rigid.  The  most  important 
part  of  the  compass  is  the  head  which,  in  the  modern  instruments, 
consists  of  two  discs  held  in  contact  in  a  fork  by  means  of  pivot 
screws.  By  adjusting  these  screws  the  pressure  between  the 
discs  is  regulated.  This  pressure  should  be  such  that  the  legs 
of  the  compass  may  be  opened  or  closed  without  springing  them. 


INSTRUMENTS  AND  MATERIALS 


139 


On  the  other  hand,  the  joint  should  be  tight  enough  to  retain 
its  setting  when  the  instrument  is  in  use. 

The  thing  of  next  importance  is  the  socket  joint  of  the 
removable  pen  and  pencil  parts.  These  are  made  in  various 
forms.  They  usually  consist  of  a  shank  on  the  pen  and  pencil 
parts  which  fits  into  a  corresponding  socket  in  the  compass  leg. 
The  proper  position  of  the  shank  in  the  socket  is  insured  by 
some  device  such  as  a  feather  or  sharp  corner  on  the  shank 


FIG.  141.     TESTING  THE  COMPASS 

which  is  matched  by  a  corresponding  slit  or  groove  in  the 
socket.  These  parts  are  made  to  clamp  together  with  a  thumb 
screw  or  else  a  bayonet  fitting  is  used. 

The  legs  of  the  compass  and  its  parts  should  move  in  the 
same  plane.  To  test  the  compass  for  alignment  place  the  parts 
in  the  sockets,  bend  the  legs  out  at  the  head,  and  then  bring  the 
joints  together,  as  shown  in  Fig.  141.  If  the  points  come  exactly 
together  the  joints  are  true. 

Before  using  a  compass  the  needle  point  and  lead  should  be 
adjusted  as  follows:  Place  the  pen  in  the  compass  and  adjust 
the  needle  point  so  that  it  projects  slightly  beyond  the  nibs  of 
the  pen.  Remove  the  pen;  replace  the  pencil  and  adjust  the 


140  MECHANICAL  DRAWING 

lead  so  that  it  is  slightly  shorter  than  the  needle  point.  The 
pen  and  pencil  parts  are  now  interchangeable  without  adjust- 
ing the  needle  point. 

The  compass  lead  should  be  sharpened  to  a  wedge  point 
similar  to  the  ruling  point  of  the  pencil.  The  width  of  the 
wedge  in  this  case  should  be  about  one-half  the  diameter  of 
the  lead. 

In  describing  a  circle  the  lower  portion  of  the  legs  should 
be  bent  so  that  they  are  perpendicular  to  the  plane  of  the  paper. 
Fig.  112.  The  compass  will  then  revolve  about  the  needle  as  an 
axis  and,  when  inking,  the  nibs  of  the  pen  will  bear  upon  the 
paper  with  equal  pressure,  which  is  a  condition  that  must  be 
fulfilled  in  order  that  the  ink  line  will  not  be  ragged. 

Before  drawing  a  circle  in  pencil  the  radius  should  be 
marked  off  on  a  center  line.  The  needle  point  should  then  be 
set  exactly  at  the  intersection  of  the  center  lines  and  the  com- 
pass adjusted  to  the  proper  radius.  The  circle  or  arc  is  drawn 
by  rotating  the  compass,  the  handle  being  rolled  between  the 
thumb  and  first  finger  of  the  right  hand.  The  lead  or  pen 
should  stop  exactly  at  the  starting  point  without  lapping  the 
line. 

The  large  compass  should  not  be  used  for  circles  of  less  than 
J"  radius.  For  very  large  circles  the  lengthening  bar  should  be 
inserted  between  the  leg  of  the  compass  and  the  pen  or  pencil 
part.  "Where  this  does  not  suffice  a  beam  compass  should  be  used. 

Dividers  are  similar  to  compasses  in  general  appearance. 
The  legs  terminate  in  sharp  steel  points.  The  dividers  are  used 
for  laying  off  distances  from  the  scale,  for  transferring  lengths, 
or  for  dividing  straight  or  curved  lines  into  any  number  of 
equal  parts. 

To  divide  a  line  into  any  number  of  equal  parts  with  the 
dividers  proceed  as  follows:  Assume  that  the  line  is  to  be 
divided  into  three  equal  parts.  (1)  Open  the  dividers  to  What 
is  estimated  to  be  one-third  the  length  of  the  line.  (2)  Step 
off  the  estimated  distance  three  times  on  the  line.  (3)  Adjust 
the  dividers  to  one-third  the  error,  making  the  distance  between 
the  points  larger  or  smaller  as  the  case  may  require.  (4)  Kepeat 
the  process  until  the  third  step  ends  exactly  at  the  end  of  the 


INSTRUMENTS  AND  MATERIALS 


141 


line.  In  taking  the  steps  the  dividers  are  held  by  the  handle 
between  the  thumb  and  first  finger  and  swung  alternately  first 
to  one  side  of  the  line  and  then  to  the  other,  as  shown  in  Fig. 
142.  This  avoids  rolling  the  handle  into  an  awkward  position 
between  the  thumb  and  finger. 

The  Bow  Pen,  Bow  Pencil,  and  Boiv  Dividers.    The  bow  pen 
and  bow  pencil  are  used  to   describe  small   circles,    and  the 


FIG.  142.    STEPPING  OFF  WITH  THE  DIVIDERS 

bow  dividers  to  lay  off  small  distances.  They  have  the 
advantage  that  they  retain  their  adjustment.  There  are  two 
forms  of  adjusting  devices,  as  shown  in  Fig.  143.  To  make 
large  adjustments  in  the  instruments  having  side  screws  the 
pressure  on  the  nut  should  be  relieved  by  pressing  the  legs 
together  with  the  left  hand  while  the  nut  is  made  to  spin  with 
the  first  finger  01  the  right  hand. 

The  Ruling  Pen  is  used  more  than  any  other  instrument  in 
the  draftsman 's  outfit  and  should  therefore  be  carefully  selected. 


142 


MECHANICAL  DRAWING 


The  steel  of  which  the  pen  is  made  should  be  properly  tempered 
and  of  such  quality  as  to  retain  a  smooth,  sharp  edge.  The 
blades  should  be  of  the  same  length,  the  inner  one  sufficiently 
stiff  to  resist  a  light  pressure  against  the  ruling  edge.  The  nibs 
should  be  of  the  same  width,  equally  rounded  and  directly  oppo- 
site each  other.  The  ends  of  the  nibs  should  be  narrow  enough 
to  give  control  in  starting  and  ending  lines  but  broad  enough 
to  hold  a  reasonable  amount  of  ink.  When  the  nibs  are  too 
narrow  the  ink  is  drawn  from  the  points  by  capillary  attraction, 
making  it  difficult  to  start  the  ink  at  the  beginning  of  a  line. 


FIG.  143.     CENTER  AND  SIDE  SCREW  ADJUSTMENT  OF  Bow  INSTRUMENTS 


For  very  long  or  heavy  lines  a  Swedish  pen  will  be  found 
convenient,  as  it  will  hold  more  ink  than  the  ordinary  pen. 

The  ruling  pen  should  be  adjusted,  filled,  and  used  in  the 
following  manner:  (1)  Adjust  the  pen  by  turning  the  thumb 
screw  to  approximately  the  proper  width  of  line.  (2)  Fill  the 
pen  by  inserting  the  quill,  attached  to  the  stopper  of  the  ink 
bottle,  between  the  nibs  of  the  pen.  Be  sure  there  is  no  ink  on 
the  outside  of  the  nibs.  (3)  Set  the  pen  to  give  the  exact 
width  of  the  line  required,  testing  it  on  the  margin  of  the  draw- 
ing or  on  a  separate  sheet.  It  should  be  tested  on  the  same 
kind  of  surface  as  that  on  which  it  is  to  be  used.  (4)  Hold  the 
pen  in  the  hand,  as  shown  in  Fig.  Ill,  with  the  first  finger 


INSTRUMENTS  AND  MATERIALS  143 

above  the  thumb  screw  and  the  second  finger  against  the  right 
side  of  the  pen.  It  should  be  held  in  a  vertical  plane,  but  may 
be  allowed  to  lean  slightly  in  the  direction  of  motion.  (5)  Draw 
rather  slowly  with  a  movement  of  the  hand  and  arm,  the  fore- 
arm remaining  perpendicular  to  the  line  being  drawn.  There 
should  be  no  wrist  movement  as  the  pen  must  not  be  rotated 
upon  its  axis.  The  tips  of  the  third  and  fourth  fingers  should 
slide  on  the  surface  of  the  T-square  or  triangle  to  steady  the 
hand.  As  the  end  of  the  line  is  approached  the  motion  of  the 
hand  and  arm  should  cease  and  the  line  should  be  completed 
with  a  finger  movement. 

The  pen  should  be  cleaned  frequently  by  inserting  a  cloth 
at  the  side  and  pulling  it  out  between  the  nibs.  This  should 
be  done  while  the  pen  is  in  use.  The  pen  should  not  be  laid 
away  until  the  surfaces  are  thoroughly  cleaned  as  ink  will 
corrode  steel.  If  the  ink  does  not  start  readily  at  the  beginning 
of  a  line  squeeze  the  nibs  of  the  pen  together  slightly  to  draw 
the  ink  down  to  the  point..  If  the  ink  has  been  allowed  to  stand 
for  some  time  the  pen  should  be  cleaned  and  refilled.  Do  not 
touch  the  pen  to  the  hand  or  a  cloth  to  start  the  ink.  Various 
devices  are  on  the  market  for  making  it  possible  to  open  a  pen 
for  cleaning  without  changing  the  adjustment.  The  best  of 
them  must  be  handled  with  care  to  avoid  changing  the  setting. 

The  pen  of  the  compass  should  be  filled,  adjusted,  and  cared 
for  in  the  same  manner  as  the  ruling  pen. 

The  nibs  of  the  pen  should  be  as  sharp  as  they  can  be  made 
without  producing  the  sensation  of  cutting  when  the  pen  is  in 
use.  They  should  not  scratch  the  paper  when  drawing  a  line. 
This  occurs  if  they  are  sharpened  to  a  point  instead  of  a  rounded 
edge,  or  if  the  point  is  rough  or  notched.  The  length  and  con- 
dition of  the  points  may  be  tested  by  holding  the  pen  up  to  the 
light  and  bringing  the  nibs  together  slowly. 

In  case  the  pen  becomes  broken  or  dull  from  use  it  should 
be  sharpened  as  follows:  (1)  Provide  a  close-grained  oil 
stone.  (2)  Close  the  nibs  until  they  just  touch  each  other. 
(3)  Hold  the  pen  on  the  stone  as  in  drawing  a  line  and 
move  it  back  and  forth,  revolving  it  slowly  in  the  plane  of 
motion  until  the  nibs  are  evenly  rounded  and  of  the  same  length. 


144  MECHANICAL  DRAWING 

Fig.  144.  This  will  dull  the  nibs.  (4)  Separate  the  nibs  and 
sharpen  them  by  rubbing  the  outside  on  the  oil  stone,  giving  at 
the  same  time  a  slight  rotary  motion  to  the  handle,  which  is  held 


FIG.  144.     SHARPENING  THE  PEN — EVENING  THE  NIBS 

at  a  small  angle  with  the  face  of  the  stone.  Fig.  145.  The 
point  of  the  pen  should  be  examined  frequently  and  the  process 
continued  until  the  nibs  are  sharp.  If  a  burr  is  produced  on  the 
inside  of  a  nib  it  may  be  removed  by  placing  the  inside  surface 
flat  against  the  oil  stone  and  rubbing  it  lightly. 


FIG.  145.    SHARPENING  THE  PEN — GRINDING  THE  NIBS 

The  Protractor  is  an  instrument  used  for  laying  off  degrees. 
It  usually  consists  of  a  semicircular  disc  of  cardboard,  brass, 
celluloid,  or  steel,  graduated  to  read  to  one  or  one-half  degrees. 
For  more  accurate  work  it  may  be  had  with  an  arm  and  a  ver- 
nier, reading  to  one  minute. 


CHAPTER  VI 

CONVENTIONS 

Line  Notation.  Through  the  medium  of  lines  a  working 
drawing  conveys  information  as  to  the  form  of  an  object.  A  line 
notation  is  therefore  necessary.  The  distinction  between  the 
lines  is  usually  made  by  varying  their  width  or  color,  or  by 
using  discontinuous  lines  with  certain  combinations  of  dashes 
and  spaces. 

In  a  pencil  drawing  the  lines  must  be  heavy  enough  to  be 
easily  seen  through  the  tracing  cloth,  but  their  widths  must  be 
approximately  the  same.  In  a  tracing,  however,  which  is  used 
in  making  a  print  for  the  workman,  a  variation  in  width  is  pos- 
sible and  assists  in  conveying  the  necessary  information. 

While  the  object  lines  should  be  noticeably  heavier  than  the 
auxiliary  lines  of  a  drawing,  the  draftsman  should  use  his 
judgment  as  to  the  width  of  each  in  any  particular  case.  In 
general  the  lines  will  be  narrower  the  more  intricate  the  detail 
of  the  drawing.  The  line  notation  given  in  Fig.  113  shows 
the  weights  of  lines  suitable  for  most  of  the  tracings  in  this 
course. 

The  following  references  will  give  definitions  and  uses  of 
the  different  kinds  of  lines  in  a  drawing: 

Object  line.     Page   111 
Dotted  line.     Pages  53,  56,  112 
Center  line.    Pages  69,  112 
Extension  line.     Pages  57,  58,  112,  184 
Dimension  line.    Pages  57,  58,  112,  184 
Crosshatch  or  Section  line.     Pages  69,  104,  112 
Broken  line.     Page  154 
145 


146  MECHANICAL  DRAWING 

All  of  the  above  lines  except  the  broken  line  are  made 
mechanically.  It  is  made  with  a  writing  pen. 

Dimensioning.  The  draftsman's  judgment  is  used  more  in 
dimensioning  than  in  making  any  other  part  of  the  drawing. 
To  avoid  mistakes  and  to  facilitate  the  work  of  the  mechanic, 
only  necessary  dimensions  should  be  given.  They  should  be 
placed  in  such  a  way  as  to  make  the  drawing  easily  read.  Cases 
are  rare  where  it  is  advisable  to  repeat  the  same  dimensions  on 
different  views.  Repeating  dimensions  adds  to  the  difficulty  in 
checking  them  and  when  changes  are  made  there  is  a  possibility 
of  making  a  change  in  one  place  and  not  in  another.  This  leads 
to  confusion.  Placing  dimensions  in  obscure  and  out-of-the-way 
places  should  be  avoided.  Whenever  possible  dimensions  should 
be  grouped  in  such  a  way  as  to  make  their  relation  obvious.  It 
should  not  be  necessary  for  the  mechanic  to  do  any  calculating 
to  obtain  necessary  dimensions. 

No  doubt  the  best  guide  to  follow  is  for  the  draftsman  to 
imagine  himself  in  the  mechanic's  place  and  to  consider  the  oper- 
ations through  which  the  object  must  go  to  become  a  finished 
product.  With  this  idea  in  mind  and  with  a  working  knowledge 
of  shop  methods,  which  every  draftsman  should  possess,  most 
problems  in  dimensioning  will  be  solved  without  difficulty.  For 
example,  when  a  machinist  drills  a  hole  he  sets  the  point  of  the 
drill  at  its  center;  hence  the  hole  should  be  dimensioned  by 
referring  its  center  to  some  surface,  line,  or  point  easily  accessible. 

In  machine  drawings  dimensions  are  usually  given  in  inches 
up  to  twenty- four  inches.  Above  twenty-four  inches  they  should 
be  given  in  feet  and  inches.  Examples:  23J",  2'— 4i". 

In  structural  drawings  all  dimensions  above  twelve  inches 
read  in  feet  and  inches.  Examples :  11$",  1' — 3 J". 

For  all  ordinary  work  fractions  in  dimensions  containing 
mixed  numbers  have  the  following  denominators:  2,  4,  8.  16,  32, 
64;  such  denominators  as  6  or  19  are  not  used.  When  very 
small  fractions  of  an  inch  are  necessary,  as  in  the  case  of 
special  fits,  etc.,  the  fractional  part  of  an  inch  may  be 
expressed  in  decimals  of  three  or  four  places.  Example:  5.006" 
bore. 


CONVENTIONS  147 

The  following  references  will  give  examples  of  dimensioning 
in  detail: 


dimension  form      Page  184 

Linear  dimensions.     Page  81 
Angular  dimensions.     Page  62 
Diametrical  dimensions.     Page  70 
Radial  dimensions.     Page  97 

Figures  and  Notes.  If  a  drawing  is  to  present  a  neat  appear- 
ance a  suitable  type,  of  letter  and  figure  should  be  used  for  all 
notes  and  dimensions.  A  very  plain  letter  should  be  selected; 
one  that  can  be  drawn  with  reasonable  rapidity  and  that  will 
be  in  harmony  with  the  remainder  of  the  drawing.  It  is  essen- 
tial that  a  standard  height  be  adopted  and  adhered  to  for  all 
notes  and  figures  on  the  drawing.  For  this  course  the  stand- 
ard height  for  the  whole  number  is  -J"  and  the  total  height  of 
the  fraction  \"  as  shown  in  Fig.  196.  Whenever  possible 
notes  should  be  lettered  on  horizontal  guide  lines.  The  letters 
should  be  •£$"  high.  To  insure  uniform  heights  for  all  notes 
the  distance  between  the  ruled  guide  lines  should  be  accurately 
laid  off  with  the  scale  or  stepped  off  with  the  dividers. 

For  the  plates  of  this  course,  up  to  and  including  those  of 
Chapter  IV,  the  vertical  Gothic  letters  and  vertical  Arabic 
numerals  will  be  used  for  all  dimensions  and  notes.  For  all  suc- 
ceeding plates  the  inclined  lower  case  Gothic  and  inclined  Arabic 
numerals  will  be  used.  As  a  rule  inclined  letters  are  used  for 
notes  in  office  practice. 

The  Title  is  usually  placed  in  a  rectangle  in  the  lower  right- 
hand  corner  of  the  sheet.  Various  elements  may  enter  into  the 
title,  depending  upon  the  character  of  the  drawing  and  the  use 
to  be  made  of  it.  The  following  items  are  usually  found  in  the 
titles  of  commercial  drawings  of  machines  or  structures. 

1.  Name  of  part  or  parts  of  machine  or  structure. 

2.  Name  of  complete  machine  or  structure. 

3.  Manufacturer's  firm  name  and  address. 

4.  Drawing  number. 

5.  Date   of  finishing  drawings. 

6.  Scale  to  which  drawing  is  made. 

7.  Initials  of  draftsman,  tracers,  and  checker. 


148 


MECHANICAL  DRAWING 


The  relative  importance  of  the  items  of  a  title  is  shown  by 
varying  the  heights  or  weight,  or  both,  of  the  letters.  In  some 
drafting  offices  a  rubber  stamp  is  used  on  the  pencil  drawing 
to  obtain  the  words  and  lines  that  are  common  to  all  drawings. 
The  same  words  and  lines  are  often  printed  on  the  tracing  cloth 
in  type.  Example:  Fig.  146.  The  style  of  letter  used  should 
be  plain  and  dignified,  whether  printed  in  type  or  drawn  free- 


PC.  no. 

PATT.  NO. 

MATEP.IAL. 

HEAT  TP/MT. 

SCALE. 

Decimal  Dimen- 



sions    must    be 
maintained. 

Sup  ... 

not   o'therwlse 

GISHOLT 

MACHINE  CO 

Or.wn. 

ChMM 

DATE 

CHAN9E  P.ICORD 

PIECE  NO. 

O.O.NO 

will  bo  allowed. 

T'"*'  

THIS  DRAWING  IN  DESIGN  AND  DETAIL  18  OUfi  PDOPCHTY 

AND  MUST  NOT  Bt  USED  EXCEPT  IN  CONNECTION  WIT, I  OUR  WORK 

ALL  RIGHTS  Of  DESIGN  OR  INVENTION  ARE  RESERVED. 


LINK-BELT  COMPANY 


PHILADELPHIA 


CHICAGO 


INDIANAPOLIS 


SCALE 


ORDER  NO. 


ESTIMATE  NO. 


J I I L 


APPROVED  BV 


CHECKED  BY 


FIG.  146.    COMMERCIAL  TITLES 


hand.     For  all  titles  in  this  course  the  vertical  capital  letters 
should  be  used. 

A  Bill  of  Material  may  be  given  on  the  drawing  or  on  a 
separate  sheet.  It  is  a  tabulated  form  in  which  such  information 
as  the  following  is  given : 

"L  Number  of  each  part  required  on  one  complete  machine 
or  structure. 

2.  Description  or  name  of  piece. 


CONVENTIONS 


149 


3.  Mark  or  number  by  which  a  piece  is  designated  on  the 
drawing. 

4.  General  drawing  number.  8.  Pattern  number,  if  cast. 

5.  Shop  drawing  number. 

6.  Erection  drawing  number. 

7.  Material  from  which  each 

piece  is  made. 


9.  Where  used. 

10.  Estimated  weight. 

11.  Order  number. 


4 


A 


m 


Shield  Plate 


Feed  Lever  Lafch  Pin 


Reach  f?0d 


Thumb  Larfch 


Feed  Lever 


. 


W.l. 


W.l, 


C.I. 


DETAILS 

FOR 
OHIO  MONARCH  SHREDDER 


34    |     359    |    A.6.S.  [SCALE-HALF  SIZE 


FIG.  147.    BILL  OF  MATERIAL 


The  bill  of  material  includes  standard  parts  such  as  bolts 
and  screws  which  are  not  detailed  on  the  drawings.  A  simple 
bill  of  material  is  shown  in  Fig.  147. 

Sectional  Views.  Very  often  a  drawing  is  not  clear  be- 
cause the  interior  of  the  object  is  complex  or  because  a 
part  of  it  is  obscured  by  other  lines.  In  such  cases  the  object 
may  be  represented  more  clearly  if  a  portion  of  it  is  imagined 
cut  away  to  expose  the  hidden  part.  The  most  common  exam- 


150 


MECHANICAL  DRAWING 


pies  of  this  method  of  representation  are:  (1)  half-section  in 
which  the  object  is  cut  into  two  similar  parts  through  an  axis 
of  symmetry,  and  (2)  quarter-section  in  which  the  object  is  cut 


Sect / on  on  AOB 

FIG.  148.    BROKEN  LINE  SECTION 


into  the  center  on  two  planes  at  right  angles.     These  sections 
are  described  in  detail  and  illustrated  on  pages  68  and  104. 


FIG.  149.    PARTIAL  SECTION 

Other  methods  of  sectioning  may  be  used,  depending  upon 
the  form  of  the  object  or  part  which  it  is  desired  to  make  clear.. 
Fig.  148  illustrates  a  case  where  the  section  is  taken  on  a  broken 
line,  AOB.  In  drawing  the  section  view,  the  cut  surface  OA 
is  considered  revolved  into  the  same  plane  with  OB.  Fig.  149 


CONVENTIONS 


151 


illustrates  what  is  called  a  partial  section.     The  ragged  line 
indicates  that  a  part  of  the  shaft  has  been  broken  away. 


FIG.  150.    REVOLVED  SECTION 

The  cross-section  of  an  object  is  often  given  by  showing  a 
revolved  section  in  one  of  the  views,  Fig.  150  or  151.     Where 


FIG.  151.    REVOLVED  SECTION 

the  section  cannot  well  be  revolved  a  line  may  be  drawn  across 
the  view  of  the  part  at  the  place  where  the  section  is  taken  and 


152 


MECHANICAL  DRAWING 


the  section  drawn  in  an  open  space  near  the  view.  Reference 
should  be  made  to  the  line  on  which  the  section  is  taken.  Fig. 
152.  Such  parts  as  spokes  or  arms  of  wheels,  solid  shafts  or 


Section  A  A 


Section  BO 


FIG.  152.    SEPARATE  SECTIONS 


FIG.  153.     SECTION  THROUGH  BIBS,  SHAFTS,  BOLTS,  ETC. 

rods,  screws,  bolts,  studs,  and  nuts  are  not  represented  as  cut 
when  the  section  plane  passes  through  their  axes.     Fig.  153. 


CONVENTIONS 


153 


Ribs  and  webs  are  not  sectioned  when  the  section  plane  is  paral- 
lel to  their  lateral  faces. 


BRICK  CONCRETE  LEATHER  WOOD 

FIG.  154.    CONVENTIONAL  CROSS-SECTIONING 

When  a  section  is  taken  through  an  assembly,  adjacent  parts 
are  crosshatched  in  different  directions  to  aid  in  distinguish- 
ing one  from  another. 


I  Rearm 


Channel  drtg/e 

FIG.  155.    CONVENTIONAL  BREAKS 


Z-Bar 


Various  combinations  of  lines  are  used  to  represent  sections 
of  different  materials.  No  standard  section  notation  has  ever 
been  universally  adopted.  It  is  customary  to  add  a  note  giving 
the  name  of  the  material  unless  a  local  section  notation  is  in 


154 


MECHANICAL  DRAWING 


use.  Except  for  a  few  cases  where  it  is  desirable  to  distinguish 
between  the  metals  in  adjacent  parts,  such  as  the  babbit  and  the 
casting  of  a  bearing,  nothing  is  gained  by  using  characteristic 
section  lines  since,  in  general,  a  note  must  be  added  to  insure 
proper  interpretation. 

Fig.  154  shows  a  few  sections  in  common  use. 

Breaks.  Where  it  is  desirable  to  omit  part  of  a  shaft  or 
rod  either  may  be  broken  and  the  break  indicated  as  shown  in 
Fig.  155.  The  ragged  line  representing  the  break  is  drawn 
freehand  in  both  the  pencil  and  the  ink  drawing. 

Screw  Threads.  The  curve  of  the  screw  thread  is  the  helix. 
It  is  generated  by  a  point  which  moves  on  the  surface  of  a 


FIG.  156.     CONSTRUCTION  OF  THE  HELIX 

cylinder  and  which  advances  uniformly  in  the  direction  of  the 
axis  of  the  cylinder  and  at  the  same  time  has  a  uniform  motion 
around  its  axis.  Fig.  156  shows  the  construction  for  the  helix. 
The  distance  in  the  direction  of  the  axis  traversed  by  a  point  in 
one  revolution  is  called  the  pitch.  Pitch  in  the  case  of  a  thread 
is  its  advance  in  the  direction  of  the  axis  in  one  revolution. 

In  Fig.  157  the  proportions  of  the  several  common  thread 
forms  are  shown  to  a  large  scale. 

The  V-thread  is  shown  in  Fig.  158  as  it  would  actually  appear 
with  the  edges  drawn  as  helices.  On  account  of  the  difficulty 
of  constructing  and  drawing  these  curves  they  are  usually  con- 
ventionalized into  straight  lines  as  shown  in  Fig.  159.  The 
method  commonly  used  for  representing  screws  up  to  about  one 
inch  in  diameter,  as  measured  on  the  drawing,  is  still  further 


CONVENTIONS 


155 


simplified  by  omitting  the  short  inclined  lines  forming  the 
"saw  teeth."  Fig.  160.  On  the  pencil  drawing  no  distinction 
is  made  in  the  weight  of  the  two  sets  of  parallel  lines  drawn 
across  the  screw,  but  on  the  tracing  it  is  customary  to  make 
a  striking  contrast  between  the  longer  and  shorter  lines  as 
shown. 


U  S.  STANDARD 


ACME. 


tstcte  af/arr?  -f-4.8 
ber'  of  f  breads  per  /nc 


Complete  threads  -F/af  tops  —Sharp  bof 


BRIGGS    STANDARD   PIPE  TH  READS  -MODIFIED 

FIG.  157.    PROPORTIONS  or  COMMON  THREAD  FORMS 

In  this  course  the  shorter  lines  will  be  made  object-line  width 
and  the  longer  lines  center-line  width.  The  angle  at  which  these 
lines  are  drawn  is  estimated.  It  remains  practically  constant  for 
all  sizes  of  standard  screws  as  the  pitch  of  the  thread  increases 
with  the  diameter  of  the  screw.  It  will  be  noted  that  the  lines 
in  the  section  view  of  the  nut  make  the  opposite  angle  to  the 
horizontal  that  those  on  the  screw  make  because  of  the  fact  that 


156 


MECHANICAL  DRAWING 


the  part  of  the  nut  shown  matches  the  invisible  half  of  the  screw. 
The  lines  are  usually  spaced  by  eye.  Guide  lines  should  be 
drawn  to  limit  the  length  of  the  shorter  lines. 

In  the  conventional  end  view  of  the  bolt,  the  circle  repre- 
senting the  outer  edges  of  the  thread  is  a  full  line,  while  one- 


FIG.    158.    Y-THREAD— SHOWING   HELICES 

half  of  the  circle  representing  the  inner  edges  of  the  thread  is 
a  dotted  line  and  the  other  half  is  a  full  line. 

In  the  conventional  end  view  of  the  nut,  the  circle  represent- 
ing the  inner  edges  of  thread  is  a  full  line,  while  one-half  of 
the  circle  representing  the  outer  edges  of  the  thread  is  a  dotted 
line  and  the  other  half  is  a  full  line. 


CONVENTIONS 


157 


FIG.  159.    V-THREAD — CONVENTIONAL  REPRESENTATION  FOR  LARGE  SIZES 


FIG.    160.     V-THREAD — CONVENTIONAL   REPRESENTATION    FOR   SMALL   SIZES 


158 


MECHANICAL  DRAWING 


A  study  of  the  relation  of  these  conventions  to  the  form  of 
the  object  should  enable  the  student  to  fix  in  mind  the  prin- 
ciples on  which  they  are  based.  With  this  relation  in  mind  it 


FIG.  161.     SQUARE  THREAD — EDGES  DRAWN  AS  HELICES 

will  be  unnecessary  for  him  to  refer  to  the  figures  in  rendering 
the  convention. 

The  United  States  Standard  (U.  S.  S.)  or  Sellers  thread, 
Fig.  157,  differs  from  the  sharp  V-thread  in  that  the  outer  and 
inner  edges  of  the  thread  are  flattened.  The  same  convention 
is  used  for  representing  it  that  is  used  for  the  sharp  V-thread. 

The  Square  Thread  is  shown  in  Fig.  161  with  the  edges  drawn 
as  helices.  Fig.  162  is  a  conventional  representation  of  the 


CONVENTIONS 


159 


screw  and   nut  in  which  the  helices   have  been  replaced  by 
straight  lines. 

For  small  sizes  the  method  shown  in  Fig.  163  is  generally 
used  because  of  its  simplicity.     The  Acme  screw  thread  is  rep- 


FIG.  162.    SQUARE  THREAD — CONVENTIONAL  [REPRESENTATION  FOR 
LARGE  SIZES 

resented  conventionally  as  shown  in  Fig.  164.  It  is  convenient 
in  drawing  to  make  the  angle  between  the  faces  of  the  thread 
30°  instead  of  29°. 

Pipe  Thread.  The  basic  form  of  the  Briggs  standard  pipe 
thread  is  that  of  the  V-thread.  This  thread  is  rounded  slightly 
at  the  outer  and  inner  edges.  A  modified  form  in  which  the 
threads  have  flat  outer  edges  and  sharp  inner  edges  is  shown 
in  Fig.  157.  This  form  is  used  by  manufacturers  because  of 


160 


MECHANICAL  DRAWING 


the  comparative  ease  with  which  taps  and  dies  are  made  for  cut- 
ting the  threads. 


FIG.  163. 

SQUARE     THREAD  —  CONVENTIONAL 
REPRESENTATION  FOR  SMALL  SIZES. 


FIG.  164. 

ACME    THREAD  —  CONVENTIONAL 
REPRESENTATION 


FIG.  165.    PIPE  THREADS — CONVENTIONAL  REPRESENTATIONS 

The  threaded  portion  of  the  pipes  tapers  one  thirty-second 
of  an  inch  in  radius  for  each  inch  of  length.  A  table  of  pipe 
sizes  is  given  on  page  265. 

Pipe  threads  are  represented  conventionally  as  shown  in 
Fig.  165. 


CONVENTIONS 


161 


Springs.    The  curve  of  the  coil  spring  is  the  helix.  Fig.  166 

shows  a  spring  in  which  the  curves  are  drawn  and  also  the 

conventional   representation   which   shows   the   curves  replaced 
by  straight  lines. 


FIG.    166.     COIL    SPRING — SHOWING    ACTUAL    AND    CONVENTIONAL 
EEPRESENTATION 

Bolts  and  Nuts.  A  bolt  consists  of  a  rod  with  a  head  on  one 
end  and  a  screw  on  the  other  to  receive  a  nut.  Fig.  167.  What 
are  known  as  United  States  Standard  bolts  arid  nuts  are  shown 


BOLT  CAP  SCREW  STUD  STUD    BOLT 

FIG.  167.    COMMON  SCREW  FASTENINGS 

in  Figs.  168  and  170.    The  proportions  given  by  the  formulae  are 
those  adopted  for  rough  boJts  .and  nuts.     The  finished  nuts  are 


162 


MECHANICAL  DRAWING 


FIG.  168.    ACTUAL  PROPORTIONS         FIG.  169.    CONVENTIONAL  REPRE- 
SENTATION 
HEXAGONAL  HEAD — U.  S.  STANDARD  BOLTS  AND  NUTS 


FIG.  170.    ACTUAL  PROPORTIONS         FIG.  171.    CONVENTIONAL  REPRE- 
SENTATION 
SQUARE  HEAD— U.  S.  STANDARD  BOLTS  AND  NUTS 


CONVENTIONS  163 

^"  less  in  width,  and  thickness  than  the  rough,  nuts.  The 
finished  heads  have  the  same  sizes  as  the  finished  nuts.  A  table 
of  standard  sizes  is  given  on  page  263»  United  States  Standard 
threads  are  used  on  these  bolts. 

Figs.  169  and  171  show  the  conventional  methods  of  rep- 
resenting hexagonal  and  square  bolt  heads  and  nuts.  Hex- 
agonal heads  and  nuts  are  usually  drawn  to  show  three  faces, 
whereas  square  heads  and  nuts  are  drawn  to  show  two  faces. 
When  this  is  done  the  hexagonal  forms  are  easily  distinguished 
from  the  square  forms. 

Since  the  proportions  of  the  head  and  nut  of  standard  bolts 
are  fixed  it  is  only  necessary  to  give  three  dimensions,  viz., 
the  length  of  the  bolt  under  the  head,  the  length  of  the  threaded 
portion,  and  the  diameter. 

A  Stud  is  a  rod  threaded  at  both  ends.  One  end  is  screwed 
into  a  threaded  hole.  The  other  end  receives  a  nut.  In  Fig.  167 
a  standard  nut  is  used. 

A  stud  placed  through  two  unthreaded  holes  with  a  nut  at 
each  end  is  called  a  stud  bolt.  Fig.  167. 

Cap  Screws  are  similar  in  form  to  bolts.  They  hold  two  parts 
together  by  passing  through  an  unthreaded  hole  in  one  and  a 
threaded  hole  in  the  other.  Fig.  167.  Heads  of  various  forms 
are  used  as  shown  in  Fig.  172. 

Machine  Screws  are  similar  to  cap  screws  in  form.  They 
differ  from  them  by  being  measured  in  decimals  instead  of  even 
fractions  of  an  inch. 

Tap  Bolts  have  the  same  form  as  cap  screws  except  that  they 
are  not  finished  before  threading,  are  threaded  for  their  full 
length,  and  are  used  for  rough  work. 

Set  Screws  are  used  ordinarily  to  prevent  relative  motion  of 
two  parts  such  as  a  pulley  and  shaft.  The  screw  is  passed 
through  a  threaded  hole  in  one  part  and  the  point  is  forced 
against  another  part.  The  proportions  of  the  set  screws  and 
the  shapes  of  the  different  points  are  shown  in  Fig.  173. 

Multiple  Threads.  It  is  sometimes  necessary  to  increase  the 
distance  traversed  by  a  nut  in  one  revolution.  If  a  coarse 


164 


MECHANICAL  DRAWING 


FLAT  COUNTERSUNK       OVAL  COUNTERSUNK          BUTTON 


D 

A 

B 

c 

E 

F 

G 

H 

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j 

K 

L 

M 

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p 

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s 

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03? 

tV 

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040 

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035 

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.  . 

i 

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a\ 

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tt 

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f 

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ft 

f 

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f 

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i 

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t 

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A 

3. 

4 

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M 

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f 

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r3, 

A 

I 

H 

A 

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f 

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£ 

1 

H 

H 

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.114 

A 

A 

M 

fi 

I 

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1 

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1A 

A 

1 

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i 

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tt 

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li 

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1 

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A 

H 

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if 

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A 

f 

fi 

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t 

i 

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1rf 

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u 

133 

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1 

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165 

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?,-Ar 

1* 

9i 

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11 

?J 

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9,i 

. 

FIG.  172.     VARIOUS  FORMS  OF  CAP  SCREW  HEADS 


CONVENTIONS 


165 


enough  single  thread  is  used  to  give  the  advance  required  the 
strength  of  the  bolt  may  be  considerably  diminished.     To  obvi- 


I      a/=  £>/a.  af  bottom 
-X-  of  ffjreaaf. 


Low  Head     Necked        Head /ess  Cup          Flat  P/rtf  Round  Pivot 

FIG.  173.    SET  SCREW  HEADS  AND  POINTS 

ate  this  difficulty  more  than  one  thread  may  be  cut  side  by  side. 
The  advance  for  one  revolution  of  a  multiple  thread  is  com- 


Sing/e  RH.  Doub/e  FtH.  Doubfe  RH.  Single  LH. 

FIG.  174.     CONVENTIONAL  EEPRESENTATION  OF  MULTIPLE  THREADS 

monly  called  the  "lead,"  and  the  pitch  is  the  distance  between 
corresponding  points  on  two  successive  threads.     Fig.  174.     The 


166 


MECHANICAL  DRAWING 


conventions  for  multiple  threads  are  distinguished  from  those 
for  single  threads  by  increasing  the  angle  of  the  cross  lines 
and  by  a  note  indicating  the  kind  of  threads  as  double,  triple, 
quadruple,  etc. 

Method  of  Indicating  Finish.  Where  and  how  a  part  is  to 
be  finished  may  be  shown  by  symbols  or  notes,  or  both.  In 
case  a  hole  is  to  be  bored,  drilled,  reamed,  cored,  etc.,  a  note  is 
usually  made  in  connection  with  the  dimension  figure.  Fig.  175. 
A  cylindrical  surface  to  be  turned,  ground,  polished,  rough 


•«  4  "Turn  *• 

h*  3"  6 

lore  «-| 

\  ' 

\ 

FIG.  175.    METHODS  OF  INDICATING  FINISH 


finished,  etc.,  may  have  the  method  of  finishing  indicated  in 
the  same  way.  In  case  all  surfaces-  of  the  object  are  to  be 
finished  and  the  method  can  be  left  to  the  workman's  judgment 
a  note  may  be  made :  FINISH  ALL  OVER.  Where  only  certain  sur- 
faces are  to  be  finished  the  character  f  may  be  placed  across  the 
lines  which  represent  these  surfaces  viewed  edgewise.  Fig.  175. 
While  the  indication  of  finish  is  a  very  small  part  of  a  draw- 
ing, it  is  nevertheless  a  very  important  detail.  The  omission 
of  a  finish  mark  may  mean  the  making  of  a  large  number  .of 
castings  from  a  pattern  on  which  no  stock  has  been  allowed 
for  finish. 


CONVENTIONS 


167 


Spur  Gears.  Fig.  176  represents  a  spur  gear  and  pinion. 
Each  is  diminished  as  it  would  be  in  a  working  drawing. 
They  are  here  drawn  in  inesh  to  show  the  relation  between  the 
tooth  circles.  The  pitch  circles,  indicated  by  P.  D.  (pitch  diam- 
eter) following  the  dimensions,  are  tangent  to  each  other  and 
form  the  basis  for  all  calculations  as  to  speed.  The  widths 
of  the  teeth  are  measured  on  these  circles,  the  width  being  equal 


Bore  /' 
50  T- 14 DP 

FIG.  176.    SPUR  GEAR  AND  PINION 


to  the  space  between  teeth  for  cut  gears.  The  distance  measured 
on  the  pitch  circle  between  corresponding  points  on  two  suc- 
cessive teeth  is  called  the  circular  pitch.  Another  common 
method  of  determining  the  spacing  of  the  teeth  is  to  give  the 
number  of  teeth  for  each  inch  of  the  pitch  diameter.  The 
diametral  pitch  for  the  gears  shown  in  Fig.  176  is  indicated  by 
the  note  14  D.  P. 


168  MECHANICAL  DRAWING 

The  distance  that  the  tooth  projects  beyond  the  pitch  circle, 

called  the  addendum,  is  expressed  by  the  fraction— 

.    ,  diametral  pitch 

or  circular  pitch        The  WQrking  paft  of  ^ 


0.141 


pitch  circle,  called  the  dedendum,  is  equal  to  the  addendum. 


FIG.  177.     CONVENTIONAL  METHOD  OF  DRAWING  SPUR  GEAR  TEETH 

The  teeth  extend  one-tenth  to  one-eighth  of  the  addendum  below 
the  dedendum  line  to  allow  clearance  for  the  teeth  of  the  mating 
gear. 

For  machine  cut  gears  the  teeth  may  or  may  not  be  drawn 
as  in  Fig.  176.    This  method  is  usually  considered  an  unneces- 


FIG.  178.    A  METHOD  or  DRAWING  ACTIONS  OF  ARMS  OF  GEARS 
AND  PULLEYS 

sary  waste  of  time.     For  cast  gears  the  teeth  are  laid  out  full 
size  to  assist  the  patternmaker. 

When  it  is  necessary  or  desirable  to  have  the  teeth  accu- 
rately constructed  Grant's  Odontograph  table  is  recommended. 


CONVENTIONS 


169 


A  conventional  method,  Fig.  177,  may  be  used  for  representa- 
tion where  accuracy  of  the  tooth  curves  is  not  essential.  Here 
the  tooth  curve  is  a  single  arc  with  a  radius  equal  to  one-fourth 
of  the  radius  of  the  pitch  circle.  After  one  center  is  located  as 
shown,  all  others  are  located  on  a  circle  drawn  through  the  first 
center. 

The  sections  of  the  arms  of  gears  or  pulleys  may  be  drawn 
as  indicated  in  Fig.  178. 


FIG.  179.     BEVEL  GEAR  AND  PINION 


Bevel  Gears.  Fig.  179  is  a  working  drawing  of  a  pair  of 
bevel  gears.  This  form  of  gears  does  not  admit  of  conventional 
representation.  The  drawing  of  bevel  gears  is  so  intimately  con- 
nected with  their  design  that  they  are  not  considered  in  this 
course. 

Worm  Gears.  As  in  the  case  of  bevel  gears  the  drawing 
of  worm  wheels  and  worms  involves  machine  design.  The 
method  of  representing  them  is  shown  in  Fig.  180. 


170 


MECHANICAL  DRAWING 

STRUCTURAL  DETAILS 


The  framework  of  bridges,  roof  trusses,  etc.,  is  a  combina- 
tion of  plates  and  rolled  structural  shapes  held  together  by 
rivets.  The  conventions  used  in  machine  drawing  must  be 
modified  for  use  in  structural  drawings  on  account  of  the 


FIG.  180.    WORM  WHEEL  AND  WORM 


peculiarities  of  these  structural  elements.  As  the  dimensions 
in  structural  details  are  often  crowded  it  is  customary  to  draw 
full  dimension  lines  and  place  the  figures  above  or  below  such 
lines.  The  object  lines  are  drawn  lighter  than  in  the  average 


CONVENTIONS 


171 


I 


n 


_L 


Artg/e 


-1 

m}'*- 

f/£^9 
<—   / 

—  >• 

1 

L 

Sa 

I     i 

I- Be  0m 


(All  dimensions  in  inches.) 


I-BEAM3 

CHANNELS 

ANGLES                                                      Z-BARS 

Depth 
of 
Beam 

n 

Depth 
of 
Chan- 
nel 

m 

Length 
of 
Leg 

111 

n 

0 

Depth 
of 
Bar 

m 

3 

4 
5 
6 
7 
8 
9 
10 
12 
15 
18 
20 
24 

CO  CO  tO 
Mt-  iM« 
(_+.COc4.^.tOtOtOtOtO»-'>-'l-' 

V 

, 

D3 

o4 

I 

3 
4 
5 
6 
7 
8 
9 
10 
12 
15 

i6 

1      toll 
lluT  to  1^ 
1A  to  If 
11    to  Ifk 
If    to  If 

l|    to2|6 

f 
H 

if 
if 

2 

I8 

if 

... 

4  to  41 
6  to  6| 

If 
2 

2! 

3 

42 

52 
6 

7 
8 

If 
If 

2 

32 
3* 

4 

....      .  . 

I 

•• 

••1  

co  to  to  to  to- 

U|>-M||- 

ii 

If 

34 
3 

FIG.  181.     DIMENSIONS  FOR  STRUCTURAL  SHAPES 


172 


MECHANICAL  DRAWING 


machine    drawing   because   the    space   between    them   is   often 
very  small. 

The  dimensions  and  other  information  for  angles,  bars,  chan- 
nels, beams,  and  plates  should  be  given  for  each  in  the  order  indi- 
cated beloAv,  referring  to  Fig.  181 : 


20  La/f.0ars 
FIG.  182.     TYPE  PROBLEM — STRUCTURAL  DRAWING 

Angles — No  Req. — Lt  X  L,  X  t  X  length,  example=2Ls- 
li"XTy,  2'— 3J"  long. 


CONVENTIONS 


173 


Z-bars— No.  Req.  D  X  LI  X  t  X  length,  example  2  zs— 5Ty  X 
3if  "  x  J">  9'— 8J'  long- 

Channels — No.  Req.  D  X  wt.  per  ft.  X  length,  example  =  3  [6 
— 8"— 11.25#,  8'— ?i"  long. 

I-beams — No.  Req.  D  X  wt.  per  ft.  X  length,  example  2  Is — 
9"— 21#,  20'— 3J"  long. 

Plates— No  Req.  Width  (inches)  X  thickness  X  length  (ft. 
and  in.),  2  Pis— 72"  X  f"  X  14'— 10J". 

The  dimensions  m,  n,  and  o,  Fig.  181,  locate  the  line  of  rivet 
centers,  or  gage  line. 

A  table  of  standard  gages  is  given  on  page  171.  Angles  are 
dimensioned  by  giving  the  length  of  the  horizontal  and  vertical 
legs  of  a  right  triangle  of  which  the  inclined  line  is  the  hypote- 
nuse. The  longer  leg  is  always  taken  as  12".  Fig.  182. 


FIG.  183.     PROPORTIONS  OF  KIVETS 

The  rivets  used  in  structural  work  are,  as  a  rule,  either 
buttonhead  or  countersunk,  having  the  proportions  shown  in 
Fig.  183.  Where  occasion  demands  it  the  buttonhead  may  be 
flattened  to  allow  for  clearance. 

Structural  work  is  usually  assembled  in  the  shop  into  con- 
venient shipping  units  and  these  .units  are  then  put  together  in 
the  field.  Fig.  184  shows  the  Osborn  rivet  code  for  distinguish- 
ing shop  and  field  rivets.  The  form  of  the  head  and  its  position 
are  also  indicated. 

Shade  Lines.  An  ordinary  working  drawing  is  made  easier 
to  read  by  the  use  of  shade  lines  which  make  certain  parts  stand 
out  in  relief.  Fig.  185. 


174 


MECHANICAL  DRAWING 


The  selection  of  lines  to  be  shaded  is  based  on  the  theory  that 
light  comes  over  the  draftsman's  left  shoulder,  the  rays  taking 
the  direction  of  the  diagonal  of  a  cube  with  its  faces  in  the 
simplest  position  with  reference  to  the  observer.  In  accordance 


Shop 


Field 


c 

> 

o 

a 

Two  fu/t  heads 


C0untersun/(  inside  (fars/de)  and  chipped 


Countersunk  outside  (nearside) and  chipped 


Countersunk  both  sides  and  chipped 


FLATTENED 


g  "high     j  'high    $  "high 


Outs/de  (nears/dej 


Both  side 


FlG.   184.      OSBORNE   ElVET   CODE 


with  this  theory  the  lines  representing  edges  which  separate 
a  lighted  from  an  unlighted  surface  should  be  shaded.  The  the- 
ory holds  for  the  front  view  only.  The  following  rule  gives  con- 
cisely the  conventional  method  for  all  views.  Shade  the  right- 
hand  and  lower  edges  of  all  surfaces. 

Other  minor  rules  are  :   (1)  Do  not  shade  the  line  of  intersec- 
tion between  visible  surfaces.     (2)   The  extreme  element  of  a 


CONVENTIONS 


175 


cylindrical  surface  should  not  be  shaded.  (3)  The  shade  line 
is  drawn  outside  the  surface  which  it  bounds.  When  a  draw- 
ing is  to  be  shaded  the  complete  drawing  is  first  inked  in  light 
lines  and  the  shade  lines  added.  A  circle  is  shaded  by  shifting 


FIG.  185.    SHADED  DRAWING 


the  center  on  a  45°  line  through  the  center  of  the  circle  a  dis- 
tance equal  to  the  width  of  the  shade  line,  retaining  a  fixed 
radius.  Small  circles  may  be  shaded  by  springing  the  bow 
instrument. 


CHAPTER  VII 

LETTERING 

Modern  practice  demands  that  the  lettering  done  on  engi- 
neering drawings  be  simple,  legiblej  and  capable  of  easy  and 
rapid  rendition.  The  simple  Gothic  style  fulfils  these  require- 
ments and  is  therefore  quite  generally  used. 

Form  and  Proportion.  A  careful  study  of  the  form  and 
proportion  of  each  letter  must  be  made  before  the  student  can 
hope  to  make  any  considerable  progress  in  lettering.  Practice 
in  drawing  the  letters  will  add  something  to  his  control  of  the 
media  with  which  he  works,  but  first  of  all  he  must  have  a  dis- 
tinct knowledge  of  what  he  is  trying  to  accomplish. 

Strokes.  For  convenience  in  forming  letters  they  are 
divided  into  strokes.  In  most  cases  the  strokes  are  natural 
divisions  of  the  outline  of  the  letter.  Three  things  should  be 
remembered  about  the  strokes  for  each  letter:  (1)  the  number 
of  strokes,  (2)  the  order  in  which  they  are  made,  (3)  the  direc- 
tion in  which  each  stroke  is  drawn.  The  advantage  in  knowing 
and  using  a  system  of  strokes  lies  in  the  fact  that  drawing  the 
letters  repeatedly  in  the  same  manner  makes  the  forming  of 
each  letter  more  nearly  automatic.  Hence  it  adds  to  the  ease 
with  which  letters  can  be  produced  and  aids  in  securing  uniform 
results. 

Spacing.  Second  only  in  importance  to  the  forms  of  the  let- 
ters is  their  relation  to  each  other.  The  best  effect  is  obtained 
when  the  areas  included  between  the  letters  in  a  word  appear 
equal.  For  the  capital  letters  the  area  of  these  spaces  should 
be  equal  to  the  area  of  a  rectangle  one-half  the  normal  width 
of  the  H.  The  space  between  words  should  be  about  three 
times  that  between  letters.  Words  set  off  by  a  comma  should 
be  spaced  from  one  to  one-half  times  the  usual  distance.  The 
space  between  sentences  should  be  about  twice  the  space  between 

words. 

176 


LETTERING  177 

The  final  test  of  good  spacing  is  legibility.  The  letters 
must  be  far  enough  apart  to  avoid  a  crowded  effect  and  yet  the 
spaces  must  not  be  so  great  that  the  letters  appear  scattered. 
In  like  manner  words  must  be  separated  enough  to  stand  out 
individually,  but  not  enough  apart  to  make  reading  difficult. 

Lettering  in  Pencil.  The  pencil  used  for  the  freehand  work 
on  a  drawing  should  be  softer  than  the  pencil  used  for  the 
mechanical  work.  It  should  be  of  such  a  grade  that  when  prop- 
erly sharpened  a  clear  gray  line  can  be  produced  with  a  single 
stroke.  It  should  not  be  hard  enough  to  cut  into  the  surface  of 
the  paper  as  difficulty  is  then  experienced  in  controlling  the  di- 
rection of  the  line. 

The  lead  should  be  sharpened  to  a  long  taper,  conical  in 
form  and  rather  blunt  at  the  end.  With  one-quarter  inch  of 
lead  exposed,  and  this  tapered  back  to  the  wood,  the  section 
of  the  lead  will  be  so  nearly  uniform  near  the  end  that  it  will 
stand  considerable  use  without  resharpening.  The  pencil  should 
be  held  in  the  hand  in  the  same  position  as  the  pen  shown  in 
Fig.  186,  with  the  forearm  nearly  in  the  direction  of  the  ver- 
tical stems  of  letters  or,  in  the  case  of  the  inclined  letters,  nearly 
in  the  direction  of  the  slant.  The  strokes  should  be  drawn  with 
a  finger  movement.  The  pencil  should  be  turned  about  its 
axis  frequently  to  keep  the  point  round  so  as  to  produce  a  line 
of  uniform  weight.  All  strokes  should  be  made  with  the  hand 
held  in  the  same  position.  Shifting  the  arm  to  obtain  advan- 
tageous positions  for  drawing  strokes  in  different  directions  is 
a  habit  which  will  prevent  the  acquirement  of  commercial 
speed  and  at  the  same  time  will  prevent  the  development  of  the 
professional  type  of  lettering  as  distinct  from  the  labored 
effect  produced  by  the  average  novice. 

Lettering  in  Ink.  The  beginner  will  find  it  more  difficult  to 
produce  satisfactory  results  with  pen  and  ink  than  with  the 
pencil  because  of  the  complications  which  arise  from  the  nature 
of  the  media.  To  secure  a  black  line  of  uniform  weight  with  a 
quick  drying  fluid  such  as  India  ink,  and  with  an  ordinary 
writing  pen,  presents  a  problem  which  usually  requires  a  care- 
ful study  of  the  methods  of  using  these  materials  and  consider- 
able intelligent  practice. 


178  MECHANICAL  DRAWING 

The  pen  should  be  held  in  the  hand  as  shown  in  Fig.  186. 
In  drawing  a  line  the  points  of  the  pen  should  be  side  by  side 
so  that  the  width  of  the  line  can  be  controlled  by  the  pressure 
applied  to  spread  the  nibs.  The  position  of  the  pen  in  the  hand 
should  not  be  changed  for  strokes  of  different  direction,  but 
rather  the  weight  of  line  should  be  kept  uniform  by  varying 
the  pressure  on  the  pen.  In  lettering  in  ink  as  in  lettering  with 
the  pencil,  the  hand  should  be  held  in  the  same  position  for  all 
strokes.  This  will  give  a  better  general  effect  and  will  make  it 
easier  to  develop  commercial  speed  in  forming  the  letters. 


FIG.  186.    CORRECT  POSITION  OF  THE  HAND  AND  PEN  FOR  LETTERING 

The  pen  should  be  filled  by  applying  the  quill  attached  to  the 
stopper  ot  the  ink  bottle  to  the  under  side  of  the  pen.  Enough 
ink  should  be  put  on  the  pen  to  last  a  reasonable  length  of  time 
and  to  produce  a  wet  line  so  that  when  it  is  dry,  enough  carbon 
will  have  been  deposited  to  make  it  black.  Overloading  the  pen, 
on  the  other  hand,  will  cause  the  corners  to  fill  at  intersecting 
lines.  The  pen  should  be  wiped  frequently  to  remove  the  dry 
ink  from  the  surfaces  of  the  pen  and  between  the  nibs.  Fresh 
ink  and  a  clean  pen  are  necessary  to  produce  sharp  clean-cut 
lines. 


LETTERING  179 

Titles.  The  title  contains  information  by  which  the  draw- 
ing can  be  identified,  such  as  the  name  of  the  part  or  parts 
of  the  machine  or  structure,  name  of  the  complete  machine  or 
structure,  manufacturer  's  firm  name  and  address,  drawing  num- 
ber, date,  scale,  and  initials  of  draftsman,  tracer,  and  checker. 

The  usual  position  of  the  title  is  in  the  lower  right-hand 
corner  of  the  sheet  where  it  does  not  interfere  with  the  drawing 
and  at  the  same  time  may  be  read  without  taking  the  sheet 
from  its  place  in  a  drawer  or  file.  The  relative  importance  of 
the  items  in  the  title  is  shown  by  varying  the  heights  and  widths 
of  the  letters  or  the  weight  of  their  stems,  or  both. 

The  lines  should  be  balanced,  i.  e.,  the  middle  point  of  each 
line  should  fall  on  the  same  vertical  line.  To  give  the  best 


at  imbtA/ 


60  Mnwv 


FIG.  187.     TITLE  MATERIAL  DIVIDED  INTO  GROUPS  OF  WORDS 

effect  the  lines  should  vary  in  length.  The  general  contour  of 
the  title  is  very  commonly  oval  or  pyramidal  in  form. 

The  arrangement  of  the  lines  of  the  title  and  the  determina- 
tion of  the  height  of  each  line  presents  a  problem  in  design 
for  the  solution  of  which  the  contour  of  the  title  should  be  kept 
in  mind. 

The  space  between  the  lines  of  letters  for  the  single  stroke 
capitals  should  be  from  three-fourths  to  one  and  three-fourths 
the  height  of  the  smallest  adjacent  letters. 

The  style  of  letter  used  for  the  title  should  be  dignified.  For 
this  reason  the  capital  letters  are  generally  used. 

The  steps  in  designing  a  title  should  be  taken  in  about  the 
following  order:  (1)  Assuming  that  the  wording  or  at  least 
the  substance  of  the  title  is  stated,  write  out  the  complete  title 
and  divide  the  words  into  logical  groups  for  the  different  lines. 
Fig.  187.  (2)  Rewrite,  tentatively  arranging  the  lines  as  they 


180  MECHANICAL  DRAWING 

will  be  in  the  printed  title.  Fig.  188.  (3)  Decide  upon  the 
relative  importance  of  the  lines  and  select  heights  of  letters 
accordingly.  It  may  now  appear  that  a  rearrangement  of  the 
lines  will  give  a  better  outline  without  affecting  the  meaning. 
(4)  The  title  may  be  balanced  by  printing  each  line  lightly  in 


(bcrand  of 


CdMxot  * 

rn       i-  ^ 

V^puiaJum^ 


/? 


FIG.  188.     TENTATIVE  ARRANGEMENT  OF  THE  LINES  OF  THE  TITLE 

its  proper  space  to  obtain  the  spacing  of  the  letters.  Any 
adjustment  necessary  to  make  the  middle  point  of  each  line  fall 
on  the  center  line  of  the  title  should  be  made.  The  letters 
should  then  be  drawn  in  full  weight.  This  method  may  be 
used  with  success  by  those  who  have  had  considerable  experi- 

CITY  OF  NEW  YORK 

BOARD  OF  WATER  SUPPLY 

OPERATING  MECHANISM 

60  INCH  GATE  VALVE 

FIG.  189.     FINISHED  TITLE 

ence  in  lettering.  The  beginner  will  obtain  better  results  with 
but  little  more  work  by  lettering  the  lines  first  on  a  trial  sheet 
to  get  the  spacing  and  then  by  using  these  lines  as  a  guide  in 
balancing  the  lines  and  spacing  the  letters  on  the  drawing,  as 
described  on  page  89.  Fig.  189  shows  a  balanced  title. 


LETTERING 


181 


In  drafting  offices  or  business  firms  where  large  numbers  of 
drawings  similar  in  general  character  are  made,  the  items  com- 
mon to  all  titles  are  very  often  printed  on  the  pencil  drawing 
with  a  rubber  stamp  and  on  the  tracing  in  type.  Uniformity  in 
treatment  is  thus  secured  and  much  time  in  lettering  is  saved. 
Fig.  146  illustrates  commercial  titles.  These  title  forms  are 
printed  on  the  under  side  of  the  tracing  cloth.  Errors  may  thus 
be  corrected  and  changes  made  in  the  lettering  done  by  the 
draftsman  without  erasing  the  printed  lines  and.  letters. 


EDGE  OF  CARD. 


BORDER  LINE 


'" 


T 


\ -MOD 


5" 


O 


FIG.  190.     LETTERING  CARD 


LETTERING  PLATES 

VERTICAL  FREEHAND  GOTHIC  CAPITAL  LETTERS  AND  NUMERALS 
PREPARATORY  INSTRUCTIONS  FOR  PLATE  1 

The  Plate.  The  first  ten  lettering  plates  will  be  in  pencil. 
Three  by  five  cards  of  the  regular  drawing  paper,  ruled  as 
shown  in  Fig.  190,  will  be  used. 


182 


MECHANICAL  DEAWING 


The  Lettering  Pencil.  Use  the  3H  pencil  for  lettering,  sharp- 
ened to  a  conical  point  as  for  freehand  sketching.  Fig.  6. 

Number,  Order,  and  Direction  of  Strokes.  Each  letter  or 
numeral  is  made  by  one  or  more  strokes.  In  general,  vertical 


STROKES 

1 

2 

3 

l> 

I 

=2 

^ 

4 

i 

...   =£.._„ 

It 

rm 

t- 

_qfr_ 

-r    | 

4' 

.....qi.:.. 

M,     _ 

i 

7 

==• 

4-7" 

FIG.  191 

and  inclined  strokes  are  made  downward  and  horizontal  strokes 
to  the  right.  Fig.  191  shows  the  number,  order,  and  direction 
of  strokes  for  the  numerals  1,  4,  7,  and  the  symbols  used  for 
the  foot,  inch,  and  dash.  The  relative  width  of  numerals  is 
shown  in  column  4. 


LETTERING  183 

The  Scale  of  Heights.  For  convenience  in  estimating  ver- 
tical distances  the  space  between  the  guide  lines  is  divided  into 
four  equal  parts.  Fig.  191. 

A  Scale  of  Widths.  The  width  of  the  H  is  taken  as  the  unit 
of  width.  This  distance  is  divided  into  four  equal  parts.  Hori- 
zontal distances  may  be  estimated  by  observing  their  relation 
to  these  divisions.  Fig.  191. 

Drawing  the  Strokes.  Before  starting  a  stroke  carefully 
plan  its  position  and  direction.  Make  each  line  with  one  move- 


3  1 

& 

1 

*/ 

II       III 

1   ) 

1 

1   1   1 

1 

^ 

Mill 

111  = 

=4 

4 

444 

4 

4 

44 

4 

141 

144  = 

=7 

7 

777 

7 

7 

7  7 

7 

147 

1747= 

=7 

7' 

7'       4   4 

4 

4 

47' 

4' 

r  74" 

17"    41= 

Z7- 

4' 

47-7" 

174-4" 

471-7" 

714-7" 

44-1"= 

FIG.  192 

ment  of  the  pencil.  A  vertical  stroke  is  made  by  drawing  a 
line  from  one  point  to  another  directly  below  it.  In  case  a  stroke 
or  letter  is  unsatisfactory  it  should  be  erased  and  redrawn. 

Foot  and  Inch  Marks.  A  short  dash  placed  to  the  upper 
right  of  a  numeral  indicates  feet.  Two  such  dashes  similarly 
placed  indicate  inches.  A  horizontal  dash  is  placed  between 
numerals  representing  feet  and  inches.  See  Fig.  191. 

DATA  FOB  PLATE  1 

Given:     Plate  1  to  reduced  size,  Fig.  192. 
Required:     To  make  the  plate  to  an  enlarged  scale. 


184  MECHANICAL  DRAWING 

Instructions: 

1.  Fasten  the  card  to  the  board  either  with  thumb  tacks  or 
by  inserting  its  corners  in  diagonal  slits  cut  in  a  larger  piece 
of  paper  which  is  tacked  to  the  board.    Fig.  190. 

2.  Draw  the  numerals  and  symbols,  using  the  number,  order, 
and  direction  of  strokes  shown  in  Fig.  191. 

3.  Write  in  the  plate  number,  followed  by  the  name  at  the 
top  of  the  sheet  as  indicated  in  Fig.  192. 


SPACE 


|C\J 

00 


\EXTENSION   LINE 

^DIMENSION  LINE 
FIG.  193.     DIMENSION  FORM  AND  ARROWHEAD 

PREPARATORY  INSTRUCTIONS  FOR  PLATE  2 

Curved  Strokes.  In  making  the  curved  strokes  of  the  5 
and  the  2  the  student  should  have  in  mind  the  form  of  the 
complete  oval. 

The  Dimension  Form.  The  dimension  form  consists  of  the 
numerals  designating  feet  and  inches,  the  foot  and  inch  marks, 
the  dash,  the  dimension  and  extension  lines,  and  the  arrowheads 
as  arranged  in  Fig.  193. 

It  will  be  seen  that  the  arrowheads  are  placed  on  the  dimen- 
sion lines  with  their  points  touching  the  extension  lines.  They 
are  composed  of  two  slightly  curved  lines  symmetrical  with 
respect  to  the  dimension  line.  The  length  of  the  arrowhead 
should  be  about  J"  and  the  width  Ty.  Fig.  193.  Fig.  194 
shows  strokes  for  arrowheads  pointing  in  different  directions. 


LETTERING 
DATA  FOE  PLATE  2 
Plate  2  to  reduced  size,  Fig.  195. 


185 


Given: 

Required:     To  make  the  plate  to  an  enlarged  scale. 

Instructions:  Proceed  as  in  Plate  1,  following  carefully  the 
number,  order,  and  direction  of  strokes. 


STROKES 


3 


WIDTH 


nu_ 


FIG.  194 

PREPARATORY  INSTRUCTIONS  FOR  PLATE  3 

Curved  Strokes.  The  oval  of  the  numeral  0  is  the  basic  form 
for  the  6  and  9.  In  making  the  outline  strokes  of  these  numerals 
the  student  should  have  in  mind  the  form  of  the  complete  oval. 


186 


MECHANICAL  DRAWING 


Whole  Numbers  and  Fractions.     The  whole   number   in   a 
dimension  will  be  made  J"  high. 


=  55555      1475      545       75457= 
=  22222      1425    5272     27527= 

TTTTTTTTTT= 


120-5" -|      [—473- 3"— 1 


FIG.  195 

The  total  height  of  the  fraction  should  be  twice  the  height 
of  the  whole  number  with  a  clear  space  between  each  numeral 


8 


FIG.  196.     SHOWING  ACTUAL  HEIGHTS  or  WHOLE  NUMBER  AND  FRACTIONS 

and  the  division  line.  Fig.  196.  To  check  these  heights  mark 
off  an  eighth  inch  and  a  quarter  inch  space  on  the  edge  of  a  card 
and  use  it  as  a  scale.  Fig.  196. 


LETTERING 


187 


DATA  FOR  PLATE  3 

Given:     Plate  3  to  reduced  size.    Fig.  198. 
Required:     To  make  the  plate  to  an  enlarged  scale. 


STROKES 


FIG.  197 


WIDTH 


00000  104  520  500  214: 
66666  460  506  672  276: 
99999  690  269  795  926: 


—  I       I       5       9  ,     17        II        Ql       ^5        ,nl 
-4     2     64      16      64      16       y2      b!6        IU2 


•I4-IOJ 


•62-9; 


16-0^— H  Z 


FIG.  198 


188 


MECHANICAL  DRAWING 


PREPARATORY  INSTRUCTIONS  FOR  PLATE  4 

The  combination  of  ovals  in  the  8  serves  as  a  basic  form  for 
the  3.  In  making  the  curved  strokes  of  these  numerals  the  stu- 
dent should  have  in  mind  the  form  of  the  complete  oval. 


STROKES 


WIDTH 


FIG.  199 


88888    418    698    785    829 
33333     136    983    568   3921 


23--9f 


'-H     J    J 


\  xi  \    J 

11 


FIG.  200 
DATA  FOR  PLATE  4. 


Given:     Plate  4  to  reduced  size.    Fig.  200. 
Required:     To  make  the  plate  to  an  enlarged  scale. 


LETTERING  189 

PREPARATORY  INSTRUCTIONS  FOR  PLATE  5 

Horizontal  and  Vertical  Strokes.  As  stated  under  Plate  1 
vertical  strokes  are  usually  made  downward  and  horizontal 
strokes  to  the  right. 


HIT 


FIG.  201.    SPACING  OF  ADJACENT  VERTICAL  STEMS 

The  direction  of  horizontal  and  vertical  strokes  must  oe  exact. 

The  relative  width  of  the  letters  is  shown  in  column  4. 
Fig.  202. 

Spacing.  In  this  and  the  following  plates  the  practice  of 
individual  letters  will  be  followed  by  the  practice  of  words.  In 
order  that  the  lettering  may  present  a  good  appearance,  it  is  as 
important  that  the  letters  be  well  spaced  as  that  they  be  properly 
formed. 

Correct  spacing  depends  more  on  the  judgment  of  the  drafts- 
man than  on  any  rule  which  might  be  given.  However,  it  may 
be  said  that  as  a  rule  the  letters  should  appear  to  be  equally 
spaced. 

For  this  style  of  letters  adjacent  vertical  strokes  should  be 
a  distance  apart  equal  to  one-half  the  width  of  the  H.  Exam- 
ple :  H  and  I,  Fig.  201.  Letters  of  irregular  form  should  be 
placed  at  such  a  distance  that  the  space  appears  equal  to  that 
between  the  H  and  I.  Example :  I  and  T,  Fig.  201. 

When  spacing  a  letter  the  beginning  of  the  first  stroke  should 
be  carefully  located. 

DATA  FOR  PLATE  5 

Given:     Plate  5  to  reduced  size.    Fig.  203. 
Required:     To  make  the  plate  to  an  enlarged  scale. 

PREPARATORY  INSTRUCTIONS  FOR  PLATE  6 

Inclined  Strokes.  Before  starting  an  inclined  stroke  th«  stu- 
dent should  sense  its  direction,  moving  the  pencil  between  its 
two  ends  without  touching  the  paper. 


190 


MECHANICAL  DRAWING 


STROKES 


II 


Fia.  202 


WIDTH 


ttfth- 


I  I  I  I  I    I  I  I  I  I    1234567890   847 
LLLLL    ILI     LIL     ILLI     ILI    LIL 
TTTTT    LIT    TILT     TILL    LIT 
HHHHH    HIT    LITH     THILL  IT 

HILT     LITH     THILL     TILT      HIT     TILL    HILL 


FIG.  203 


LETTERING 

DATA  FOR  PLATE  6 

Given:     Plate  6  to  reduced  size.    Fig.  205. 
Required:     To  make  the  plate  to  an  enlarged  scale. 


STROKES 


I 


II 


WIDTH 


E 


FIG.  204 


191 


6 

FFFFF  LIFT  FIFTH  FIT  IF 
EEEEE  FILLET  FILE  TELL 
NNNNN  FIN  NINETEEN  FIN 
MMMMM  ELEMENT  LIMIT 


FEET   TENTH    MILE    NINE   LIME   FILM  \ 


PIG.  205 


192 


MECHANICAL  DRAWING 


STROKES 


I 


FIG.  206 


WIDTH 


MM 


KKKKK  KILN  KEEL  KINK  : 
YYYYY  KEY  FLY  KNEEL  I 
ZZZZZ  MIZZEN  ZENITH  : 
AAAAA  FALL  LATHE  LAY: 

LAZY    METAL     KENT     KNIFE    KINK     KEY  : 


FIG.  207 


LETTERING  193 

PREPARATORY  INSTRUCTIONS  FOR  PLATE  7 

As  stated  under  Plate  6,  the  student  should  sense  the  direc- 
tion of  an  inclined  stroke  before  drawing  it. 

KEY 

FIG.  208.    SPACING  OF  IRREGULAR  FORMS 

The  spacing  between  irregular  letters  should  appear  equal 
to  the  area  of  one-half  the  H.  Fig.  208. 

DATA  FOR  PLATE  7 

Given.    Plate  7  to  reduced  size.    Fig.  207. 
Required:     To  make  the  plate  to  an  enlarged  scale. 

DATA  FOR  PLATE  8 

Given :     Plate  8  to  a  reduced  size.    Fig.  211. 
Required:     To  make  the  plate  to  an  enlarged  scale. 

PREPARATORY  INSTRUCTIONS  FOR  PLATE  9 

The  letter  0  is  wider  than  the  numeral  0. 

The  forms  of  the  Q,  C,  and  G  are  based  on  the  oval  of  the  0. 

Spacing  Curved  Stroke  Letters.  As  stated  in  Plate  5,  the 
area  included  between  the  contour  of  two  adjacent  letters  should 
appear  equal  to  the  area  of  one -half  of  the  H.  When  a 
vertical  stroke  and  a  curved  stroke  are  properly  spaced  the 
clear  distance  between  them  is  slightly  less  than  one-half  the 
width  of  the  H.  Example :  The  I  and  O,  Fig.  209. 


TSb 


FIG.  209.      SPACING  OF  CURVED  FORMS 

The  clear  distance  between  two  curved  strokes  will  be  less 
than  that  between  vertical  and  curved  strokes.  Example:  The 
0  0  in  Fig.  209. 


STROKES 


TIE 


FIG.  210 


WIDTH 


NIIII 


zVVVVV  VALVE  LEVEL  LEVEL 
zWWWWW  WYE  WHEEL  FEW 
zXXXXX  LYNX  FIX  EXTENT 
zUUUUU  MINIMUM  MAXIMUM 
I  J  J  J  J  J  AJAX  JAM  FAULTY 


(194) 


Fio.  211 


STROKES 

WIDTH 

1 

2 

3 

! 

I 

<x  — 

( 

3 

0 

J 

jll 

\ 

[C 

-/  — 

( 

J 

C 

Pfc 

fl- 

'          I    . 

I 

-/  — 

C 

N_ 

t 

\ 

A... 

>» 

{II 

i 

I 

: 

I 

v  — 

C 

? 

[ 

"N  

r 

y 

7 

in 

! 

i 

! 

6 

D' 

D 

|H 

! 

FIG.  212 


OOOOO  ONYX  AVIATION  1  = 
OOQQO  QUAIL  ANTIQUITYz 
CCCCC  CHEQUE  CONNECTION  = 
GGGGG  ENGINE  GAUGE  T-S^'Z 
DDDDD  LADLE  HEAD  FLOAT  = 


FIG.  213 


(195) 


STROKES 


I 


IP: 


=s. 


B 


V- 


FIG.  214 


WIDTH 


H 


zPPPPP  PITCH  DIAM  PATCH 
zRRRRR  ROD  RULE  ARMATURE 
zBBBBB  BEARING  BUILDER  BIN 
zSSSSS  SCREW  PISTON  FOR  4 
Z&&C&&C&  SCOTT  &c  JONES 


(196) 


.  215 


LETTERING  197 

When  spacing  a  letter  having  a  curved  outline  the  begin- 
ning of  the  first  stroke  should  be  carefully  located.  In  planning 
the  letter  the  clear  space  between  it  and  the  previous  letter 
should  be  held  in  mind. 

DATA  FOR  PLATE  9 

Given:     Plate  9  to  reduced  size.    Fig.  213. 
Required:     To  make  the  plate  to  an  enlarged  scale. 

PREPARATORY  INSTRUCTIONS  FOR  PLATE  10 

The  first  two  strokes  of  the  P,  R,  and  B  are  exactly  alike. 
The  basic  form  of  the  S  is  a  combination  of  two  ovals.  When 
drawing  the  strokes  of  the  S  these  ovals  should  be  held  in  mind. 

DATA  FOR  PLATE  10 

Given:     Plate  10  to  a  reduced  size.    Fig.  215. 
Required:     To  make  the  plate  to  an  enlarged  scale. 

LETTERING  IN  INK 
PREPARATORY  INSTRUCTIONS  FOR  PLATE  11 

The  following  is  a  list  of  the  materials  used  in  making  let- 
tering plates  in  ink. 

1.  Tracing  Cloth,  4"  X  6"  sheets. 

2.  One  of  the  following  or  any  similar  pen  which  will  give 
satisfactory  results  may  be  used: 

303  Gfflott's 

404  Gfflott's  |r™ 

.  _          j^Three  of  each. 
Spencerian  Nc.  1 

Lady  Falcon 

3.  Penholder. 

4.  Black  waterproof  drawing  ink. 

Square  one  of  the  three  by  five  inch  cards  on  the  board  and 
stretch  the  tracing  cloth  over  it  with  the  dull  side  up.  The 
surface  of  the  cloth  should  be  prepared  for  inking  by  being 
rubbed  with  chalk  dust.  All  superfluous  chalk  must  be  removed 


198  MECHANICAL  DRAWING 

to  prevent  its  clogging  the  pen.  The  guide  lines  for  the  letters 
should  be  drawn  on  the  cloth  in  pencil.  When  the  plate  is 
finished  a  border  rectangle  should  be  drawn  and  the  sheet 
trimmed  to  3"  X  5".  Fig.  190.  The  space  outside  the  cutting 
lines  may  be  used  to  try  the  pen  on  during  the  process  of  let- 
tering the  plate.  A  pen  should  be  selected  which  will  give  a 
width  of  line  suited  to  the  height  of  letters  to  be  made.  The 
proper  width  of  line  should  be  secured  with  but  little  spreading 
of  the  nibs  of  the  pen.  Fig.  186  illustrates  the  position  of  the 
pen  in  the  hand  while  lettering.  Note  that  the  forearm  is  nearly 
parallel  to  the  vertical  strokes.  Vertical  strokes  should  be  made 
with  a  finger  movement.  In  making  the  horizontal  and  curved 
strokes  this  movement  is  combined  with  a  turn  of  the  wrist. 

ROUGH   ROUND   RODS 
OHIO  CORLISS   ENGINE 

FIG.  216.    EXAMPLES  OF  WORD  SPACING 

To  fill  the  pen,  place  the  ink  on  the  under  side  by  means  of 
the  quill  attached  to  the  stopper  of  the  bottle.  The  stopper 
should  be  returned  to  the  bottle  since  the  ink  dries  rapidly. 

Composition.  In  this  and  the  following  plates  in  lettering 
words  will  be  combined  into  phrases  and  sentences.  The  spac- 
ing of  words  plays  an  important  part  in  securing  a  good  general 
effect  in  a  line  of  letters.  The  space  between  words  should 
appear  equal  to  three  times  that  between  letters  or  one  and  one- 
half  times  the  width  of  the  H.  Adjacent  vertical  strokes  will 
therefore  be  separated  by  a  space  one  and  one-half  times  the 
width  of  the  H.  The  clear  distance  between  two  words  having 
vertical  strokes  adjacent  to  a  curved  stroke  will  be  less  than  one 
and  one-half  times  the  width  of  the  H.  The  clear  distance 
between  two  words  having  adjacent  curved  strokes  will  be  still 
less.  Example :  See  Fig.  216. 

DATA  FOR  PLATE  11 
Given:     Plate  11  to  reduced  size.    Fig.  217. 


LETTERING  199 

Required :  To  make  the  plate  to  an  enlarged  scale.  In  this 
plate  the  wording  of  the  titles  for  the  first  pencil  mechanical 
drawing  plates  is  used.  The  letters  are  approximately  the  height 
used  in  the  title. 


Gtab// 

CLAMP  TENSION  WEIGHING  FIXED 
FULL  SIZE  YOKE  BLOCK  LOCOMOTIVE 
VALVE  MOTION  SCALE  FULL  SIZE 

ANGLE  TENSION  WEIGHING  FIXTURE 
FULL  SIZE  CORE  REAM  PLATE  GIRDER 


FIG.  217 


FOUNDATION    WASHER    CORE 

ENGINE    BED     SCALE    FULL    SIZE      BACK 
REST      24    TURRET    LATHE      SCALED 

JOURNAL    BEARING    ELECTRIC 

RAILWAY    MOTOR    CAR    SCALE   HALF  SIZE 


FIG.  218 


200  MECHANICAL  DRAWING 

DATA  FOR  PLATE  12 

Given:     Plate  12  to  reduced  size.    Fig.  218. 

Required:  To  make  the  plate  to  an  enlarged  scale.  The 
words  in  this  title  are  the  same  as  those  used  in  the  second 
mechanical  drawing,  Plate  15. 


BRUSH    HOLDER     BRACKET 

PRESSURE    TUNNEL    CABLE   REEL      JIG 

FULL  SIZE       HINGE     BRACKET 

CASING    OIL    COVER       OPERATING    CAM 

CLUTCH    LEVER    BRACKET 


FIG.  219 


BASE    PLATE    FOR  CABLE  REEL 

MOTOR      I  WANTED  -  CAST    IRON      SCALE 
QUARTER    SIZE          MANHOLE       FOR 
CATSKILL    AQUEDUCT    CONDUIT        CAST 
IRON     21  WANTED      SCALE-HALF     SIZE: 


FIG.  220 


LETTERING 


201 


DATA  FOR  PLATE  13 

Given:     Plate  13  to  reduced  size.    Fig.  219. 

Required:  To  make  the  plate  in  ink  to  an  enlarged  scale. 
The  words  in  this  title  are  the  same  as  those  used  in  the  third 
mechanical  drawing,  Plate  17. 

DATA  FOR  PLATE  14 

Given:     Plate  14  to  reduced  size.    Fig.  220. 
Required:     To  make  the  plate  in  ink  to  an  enlarged  scale. 
The  words  used  in  this  title  are  the  same  as  those  used  in 
the  first  tracing,  Plate  19. 


CLUTCH    BRACKET    PRESSURE: 

TUNNEL    HOISTING    CAGE         2   WANTED  I 
CAST     IRON       SCALE  -  QUARTER    SIZE    ! 

MOTOR     BRACKET  FOR  VALVE: 

OPERATING    MECH.     SCALE-HALF    SIZE! 


FIG.  221 
DATA  FOR  PLATE  15 

Given:     Plate  15  to  a  reduced  size.    Fig.  221. 
Required:     To  make  the  plate  in  ink  to  an  enlarged  scale. 
The  words  used  in  this  title  are  the  same  as  those  used  in 
the  second  tracing,  Plate  21. 

PREPARATORY  INSTRUCTIONS  FOR  PLATE  16 

Composition.  This  and  the  following  plates  will  be  devoted 
to  the  practice  of  notes  which  frequently  appear  on  the  drawing 
to  give  information  not  shown  by  the  views. 


202  MECHANICAL  DRAWING 

DATA  FOR  PLATE  16 

Given:     Plate  16  to  reduced  size.    Fig.  222. 

Required:     To  make  the  plate  in  ink  to  an  enlarged  scale. 


z  CORE    FOR    I"   FOUNDATIONS 

~  BOLT      BORE    2f"  FOR    2^   SHAFT   FORZ 

z  NOS.  I.2.3.&.4      12"  SHEAVE     COREZ 

Z  TAPPED    FOR   f"-ll    SET   SCREW      PIVOTZ 

zMILL    THIS    END    ONLY  TURNZ 


FIG.  222 


z  OPERATING  CAM  A  12  AS  z 
z  SHOWN  PATTERN  *M7l83Lz 
z  REVERSE  PATTERN  #819  Rz 


Z  DRILL    FOR          i       SPRING    COTTER    A.34Z 
I  CROWN    NUT    FOR    PIN    FOR    I&.4       CORE! 


FIG.  223 

DATA  FOR  PLATE  17 

Given:    Plate  17  to  reduced  size.    Fig.  223. 
Required:     To  make  the  plate  in  ink  to  an  enlarged  scale, 


LETTERING  203 

DATA  FOR  PLATE  18 

Given:     Plate  18  to  reduced  size.    Fig.  224. 
Required:     To  make  the  plate  to  an  enlarged  scale. 


BORE   2"  ON   ALL   FUTURE 
ORDERS    BOTH    NEW    AND 
REPAIR    IRRESPECTIVE    OF 
WHAT    ORIGINAL    ORDER 
CALLS    FOR    STANDARD  WASHER 

PIG.  224 


=END    OF   STUD   TO  BE   FLATz 
zTENED   AND  CAST   IN   PARTz 

Z  USE   FILLERS    513   TO    ALLOW   GEARS   TOZ 
ZMESH    PROPERLY.     CROSS   HEAD   PIN  ASZ 

ZSHOWN       CROSS    HEAD   PIN     z 

FIG.  225 
DATA  FOR  PLATE  19 

Given:     Plate  19  to  reduced  size.    Fig.  225. 
Required:     To  make  the  plate  to  an  enlarged  scale. 


204  MECHANICAL  DRAWING 

DATA  FOR  PLATE  20 

Given :     Plate  20  to  reduced  size.    Fig.  226. 
Required:     To  make  the  plate  to  an  enlarged  scale. 


:2'-l|xl9|"    ROUGH    ROUND    RODS     DRILL    I 

:  14-24   FLAT    HEAD    SCREW: 

:f"-ll    BOLTS- 6^"   LONG    WITH    NUT    AND 
:CHECK    NUT       |"-I6    ROUND    HEAD   BOLT: 

CONNECTING    ROD  BEARING: 


FIG.  226 


Z2    FILLER    PLATES    £ x  9"x  2- 4"          REAM 
Z  2    PIN    PLATES    INSIDE    {xH'x2'-6"       JIG 
Z2    HINGE    PLATES    OUTSIDE    £x|0"x2" 
Z  LATERAL    PLATE    {x20"x|'-o|'  ALL 

Z  HOLES    £       COUNTERSUNK    |"        RIVETS 

FIG.  227 

DATA  FOE  PLATE  21 

Given :     Plate  21  to  reduced  size.    Fig.  227. 
Required:     To  make  the  plate  to  an  enlarged  scale. 


LETTERING  205 

DATA  FOR  PLATE  22 

Given :     Plate  22  to  reduced  size.    Fig.  228. 
Required:     To  make  the  plate  to  an  enlarged  scale. 


4  CHANNELS  I2"xl4'-8|"  ROOF  TRUSS: 
I  COAT  OF  GRAPHITE  PAINT  DRILL  {: 
I2  HOLES  EQUALLY  SPACED  TO  FIT 

PIECE  NO,  ii7  PISTON  FOR  10  : 
H.  R  HORIZONTAL  ENGINE  : 

FIG.  228 


Z     A   DRAWING,    THE    MECHANICAL    PART 
ZOF    WHICH    IS    WELL    EXECUTED     MAY 
Z  HAVE    ITS    APPEARANCE    SPOILED    BY 
ZPOOR    LETTERING      MAKE    THE    LAST 
Z  PLATE    THE    BEST    OF    ALL     123456 

FIG.  229 

DATA  FOR  PLATE  23 

Given:     Plate  23  to  reduced  size.    Fig.  229. 
Required:     To  make  the  plate  to  an  enlarged  scale. 


206  MECHANICAL  DRAWING 


THE   OBJECT   OF    THE    DRAWING    IS 
ZTO   CONVEY    TO    THE    SHOP    WHAT   THE 
ZDRAFTSMAN    WANTS,-  TIME    SPENT 

ZON    THE    DRAWING    OFTEN    SAVES 
IIMUCH    VALUABLE    TIME    IN    THE    SHOP. 


ONE    OF    THE    ESSENTIALS    OF    GOOD 
"LETTERING    IS    A    THOROUGH    UNDER- 
"STANDING    OF    THE    RELATIVE     PRO- 
"PORTIONS    OF   THE    DIFFERENT     PARTS 
ZOF    EACH    LETTER, 


LETTERING  207 


INCLINED   FREEHAND  LOWER   CASE  LETTERS  AND 

NUMERALS 

PREPARATORY   INSTRUCTIONS   FOR   PLATE   1 

The  Slope  of  the  inclined  letters  is  equal  to  that  of  the 
hypotenuse  of  a  right  triangle,  the  vertical  leg  of  which  is  two 
and  one-half  units  long  and  the  horizontal  leg  one  unit  long. 
Fig.  230. 

Lettering  in  Ink.  The  following  list  of  plates  will  be  made 
in  ink  directly  on  tracing  cloth.  A  list  of  materials  needed 
and  directions  for  lettering  in  ink  are  given  for  Plate  11  of 
the  vertical  Gothic  letters. 


208 


MECHANICAL  DRAWING 


SLOPE 


STROKES 


STROKES 


•A 


=' 


IL 


lllll 


L 


lllll 


I 


IL 


"I 


i 


n. 

lllll 


lllll 


HUH 


H 111- 


FIG.  230 


LETTERING 


209 


STROKES 


STROKES 


I. 


V. 
Hill 


Illl'l 


III 


mil 


//// 


t 


'i 


inn 


'///I 


77- 


///.. 

L 


IIWI 


-77" 

iiir 


//// 


'IIH 
'f/ffi 


'Illl 


uiif 


Wi 


Wl 


FIG.  231 


210  MECHANICAL  DRAWING 

DATA  FOE  PLATE  1 

Given:    Plate  1  to  reduced  size.    Fig.  232. 
Required:     To  make  the  plate  to  an  enlarged  scale. 


=  1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 

=  444444  I4H   4114   441  /4/ 

=  777777  174  147  4711  4177 
=  222222  1247  1724  22274 
=  555555  1572  5522  14725 

FIG.  232 


000000  1470  7104  20504 
666666  1626  6064  65276 
999999  1929  4956  9/979 

15    19    13    I    I     7     5    3    2      9.      1 
16    32    64   2    4     8     8     4     16     32     8 

1116   47OI   2/96    1245  790 

PIG.  233 


LETTERING  211 

PREPARATORY  INSTRUCTIONS  AND  DATA  FOR  PLATE  2 

Curved  Strokes.  The  6  and  9  have  the  same  oval  outline 
as  the  0.  This  form  should  be  kept  in  mind  while  drawing  the 
6  and  9. 

Given:     Plate  2  to  reduced  size.    Fig.  233. 
Required:     To  make  the  plate  to  an  enlarged  scale. 

PREPARATORY  INSTRUCTIONS  AND  DATA  FOR  PLATE  3 

The  two  ovals  of  the  8  have  their  major  axes  at  45°.  The 
same  combination  of  ovals  is  the  basic  form  for  the  3. 


=  33333333  323  4353  363  = 
=  88888888  1834  687  585  = 
zssssssssss  1473  386  83= 

=  <  Z359^3_17_- 

.ssssss  6  4  Q  I6  64-  4  IQ  - 
=  1830  1492  123456789= 


FIG.  234 

Given:     Plate  3  to  reduced  size.    Fig.  234. 
Required:     To  make  the  plate  to  an  enlarged  scale. 
The  strokes  for  the  S  are  given  in  Fig.  243. 

PREPARATORY  INSTRUCTIONS  AND  DATA  FOR  PLATE  4 

Spacing  of  Letters.  Observe  carefully  the  spacing  of  the 
letters  in  the  words.  Correct  spacing  is  as  essential  as  correct 
forms. 


212 


MECHANICAL  DRAWING 


STRC 

)KES 

1 

2 

/ 

7 

ft 

'? 

—  // 

// 

'"=/'" 

'••"§/?" 

3 

FIG.  235 


-J 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 


:  /  /  /  /  /  /  /  /  /  /  ///  ///  ///  ///  ///  /// 


vvvvvvvv    liv   vilt  liv   vilt  till 

yyyyyyyy  My  iyy  ^y  ivy  m 


FIG.  236 


Given:     Plate  4  to  reduced  size.    Fig.  236. 
Required:     To  make  the  plate  to  an  enlarged  scale. 


LETTERING 


213 


STROKES 


2  3 


STRC 

KES 

I 

2 

/ 

...... 

$ 

3W 

& 

/? 

7 

/V—- 

-Ji- 

/ 

•f- 

-f 

FIG.  237 


w  w  w  w  w  will  wily  wilt  twit  it 
k  k  k  k  k  k  kilt  kitty  z  z  z  z  z  tiz 
x  x  x  x  x  x  vix  xylyl  viz  xylyl  ill 

J  J  J  J  J  J  jilt  JiH  Jill  jilt  Jill  jilt  it 
f  f  f  f  f  f  fizz  jiffy  flit  fizz  fifty 


FIG.  238 


DATA  FOR  PLATE  5 


Given:     Plate  5  to  reduced  size.    Fig.  238. 
Required:     To  make  the  plate  to  an  enlarged  scale. 


214 


MECHANICAL  DRAWING 


£ 


STROKES 


•^V 


iff. 


FIG.  239 


^rV 


~i.rrrrrrr  kirk  vitrify  kirts  six  z 
~  h  h  h  h  h  h  hilt  whirl  whist  his  z 
~  n  n  n  n  n  n  hint  lynx  hint  lynx  z 
~  m  m  m  m  mink  hymn  milk  hint  ~ 

~7" 
O  O'         /~>  /  I          I 

_r — 23    Q — H    r~ 


o" 

65-4?- 


FIG.  240 

DATA  FOE  PLATE  6 

Given:     Plate  6  to  reduced  size.    Fig.  240. 
Required:     To  make  the  plate  to  an  enlarged   scale. 


LETTERING 


215 


PREPARATORY   INSTRUCTIONS 
AND  DATA  FOR  PLATE  7 

Curved  Strokes.  The  major 
axes  of  the  oval  letters  of  this 
plate  are  in  the  direction  of  the 
slope. 

Given:  Plate  7  to  reduced 
size.  Fig.  242. 

Required:  To  make  the 
plate  to  an  enlarged  s^ale- 


STROKES 


m 


=n 


FIG.  241 


u  u  u  u  u  u  u    hum  tumult  funny 
o  o  o  o  o  o  o  moon  form  fourth 
c  c  c  c  c  c  c   lock  column  corks 
e  e  e  e  e  e  e   clever  come  fewer 
68 j"  29'-ol"  /3/j"      997' -8 


FIG.  242 


216  MECHANICAL  DRAWING 

PREPARATORY  INSTRUCTIONS  FOR  PLATE   8 

Curved  Strokes.    The  major  axes  of  the  ovals  of  this  plate 
make  45°  with  the  horizontal. 


STROKES 


STROKES 


FIG.  243 


a  a  a  a  a  a  crank  make  chairs  : 
d  d  d  d  d  d  round  drain  rods  at 
q  q  q  q  q  quail  g  g  g  g  ground  : 
b  b  b  b  b  b  bearing  block  blade  : 
p  p  p  p  p  p  pipe  faceplate  shape'. 


FIG.  244 


LETTERING  217 

DATA  FOR  PLATE  8 

Given:     Plate  8  to  reduced  size.    Fig.  244. 
Required:     To  make  the  plate  to  an  enlarged  scale. 

PREPARATORY  INSTRUCTIONS  FOR  PLATE   9 

Composition.  In  the  following  composition  plates  the  spac- 
ing of  letters  and  words  should  be  given  as  much  consideration 
as  the  forms  of  the  letters.  The  student  should  strive  to  pro- 
duce a  good  general  effect  in  the  plate. 


-  Drill       Ream  I"  Bore  2"  Holes 
~fo  Suit  Motor  Used  End  ofsfud 
~fo  be  flattened  and  cast  in  part 
=  /    Use  Fillers   513   to  Allow  A// 
~  Gears  to  Mesh  Properly    Head 


FIG.  245 

DATA  FOR  PLATE  9 

Given:     Plate  9  to  reduced  size.    Fig.  245. 
Required :     To  make  the  plate  to  an  enlarged  scale. 


218  MECHANICAL  DRAWING 

DATA  FOR  PLATE  10 

Given:     Plate  10  to  reduced  size.    Fig.  246. 
Required:     To  make  the  plate  to  an  enlarged  scale. 


2-lj*x  /9J"  Hough  Round  Rods 
/-//  Bolts-  6^'  Long  Without 
Nut  &.  Check  Nut      Connecting 
Rod  Bearing    14  -  24  Flat  Hea 
Machine  Screw    Graphite  Paint 


FIG.  246. 


z  I"  Drill  and  Ream  Holes  for  All  z 
^.Pieces,  Spring  Must  Deflect  2"  z 
z  Factor  of  Safety  1,  5  Patterns  ~ 
z  I  j"  Core  for  Piece  No,  640139  z 
=  f  'Chain  (277  Links)  Material^. 

FIG.  247 

DATA  FOE  PLATE  11 

Given:     Plate  11  to  reduced  size.    Fig.  247. 
Required:     To  make  the  plate  to  an  enlarged  scale. 


LETTERING  219 

DATA  FOR  PLATE  12 

Given:     Plate  12  to  reduced  size.    Fig.  248. 
Required:     To  make  the  plate  to  an  enlarged  scale. 


Groove        R  in  finished  face, 


=  Drill  for  /  '  Split  Cotter,  1914-15= 
=  A//  Fillets  £  R  Unless  Otherwise^ 
^Specified,  Key  for  9"  Spur  GearL 
-  "x  8  "  Stud  Bolt  Nut,  1915  -16= 


FIG.  248 


=  Make  Oil  Tight    Drill  for  No,  I6 

~  Standard  Flat  Head  Machine 

—  i" 

^L  Screw,     3^    Lock  Nut   Washer 

z  These  Holes  in  Piece  No,   64/8 L 
^LOnly     Drawing  No,   166,     Piece 

FIG.  249 

DATA  FOR  PLATE  13 

Given:     Plate  13  to  reduced  size.    Fig.  249. 
Required:     To  make  the  plate  to  an  enlarged  scale. 


220  MECHANICAL  DRAWING 

DATA  FOR  PLATE  14 

Given:     Plate  14  to  reduced  size.    Fig.  250. 
Required:     To  make  the  plate  to  an  enlarged  scale. 


Round  Point  Set  Screw  -  Brass 

/" 
/  Required,      Tap  2^    Special 

^0    Threads  per  I"         Bottom 
Spring  Plate   Brass  -Finish  -/ 
Required,    Outside  Finish  All  Over 


FIG.  250 


A  careful  study  of  the  form 
proportion  of  each  letter 
~musf  be  made  before  the  sfu- 
^.dent  can  hope  to  make  any 
^siderable  progress  in  lettering 

FIG.  251 

DATA  FOB  PLATE  15 

Given:     Plate  15  to  reduced  size.    Fig.  251. 
Required:     To  make  the  plate  to  an  enlarged  scale. 


LETTERING  221 

DATA  FOE  PLATE  16 

Given:     Plate  16  to  reduced  size.    Fig.  252. 
Required:     To  make  the  plate  to  an  enlarged  scale. 


For  convenience  in  forming 
the  letters  they  are  divided  into : 
strokes,      Three  things  should  be~_ 
remembered  about  the  strokes    : 
for  each  letter,  (I)  the  number-'. 


FIG.  252 


~of  strokes  (2)  the  order  in  w  hie  h 
^.they  are  made  (3)  the  direction 
z//7  which  each  stroke  is  drawn, 
~     Second  only  in  importance  to 
forms  of  the  letters  is  their 


FIG.  253 
DATA  FOR  PLATE  17 

Given:     Plate  17  to  reduced  size.    Fig.  253. 
Required:     To  make  the  plate  to  an  enlarged  scale. 


MECHANICAL  DRAWING 

DATA  FOR  PLATE  18 

Given:     Plate  18  to  reduced  size.    Fig.  254. 
Required:     To  make  the  plate  to  an  enlarged  scale. 


relation  to  each  other,    The  final 
test  of  good  spacing  is  legibility, 
A  II  strokes  should  be  made 
the  hand  and  arm  in  the 
position,    123456  789 


FIG.  254 


Shifting  of  the  arm  to  obtain 
^.advantageous  positions  for 
^.ing  strokes  in  different  direct- 
~/or?s  /s  a  habit  which  will  neve 
~  lead  to  rapid  production  of- 

FIG.  255 

DATA  FOE  PLATE  19 

Given:     Plate  19  to  reduced  size.    Fig.  255. 
Required:     To  make  the  plate  to  an  enlarged  scale. 


LETTERING  223 

DATA  FOE  PLATE  20 

Given:    Plate  20  to  reduced  size.    Fig.  256. 
Required:     To  make  the  plate  to  an  enlarged  scale. 


-letters  and  at  the  same  time 
.it  will  prevent  the  development 
.of  the  snap  and  swing  which 
.gives  the  character  to  what  is 
'.recognized  as  good  lettering, 


FIG.  256 


z    A  drawing,   the  mechanical 
lipart  of  which  is  well  executed, 

have  its  appearance  spoiled 
poor  lettering,  Lines  should 
black  and  of  uniform  weight, 


FIG.  257 

DATA  FOR  PLATE  21 

Given:     Plate  21  to  reduced  size.    Fig.  257. 
Required:     To  make  the  plate  to  an  enlarged  scale. 


224  MECHANICAL  DRAWING 

DATA  FOR  PLATE  22 

Given:     Plate  22  to  reduced  size.    Fig.  258. 
Required:     To  make  the  plate  to  an  enlarged  scale. 


:    Careful  attention  to  detail  com 
\bined  with  intelligent  and  per- 
\sistent  practice  will  do  much  to 
.offset  lack  of  talent  for  lettering 
2357   9861   45309    728695 

TIG.  258 


CHAPTER  VIII 

ADVANCED  DRAWING 

DRAWING  FROM  MODELS — DETAIL  DRAWING — ASSEMBLY 
DRAWING 

» 
PREPARATORY  INSTRUCTIONS  FOR  PLATE  24 

Irregular  Curve.  A  curved  line  which  is  determined  by  a 
series  of  points  may  be  drawn  with  the  irregular  curve.  When 
the  points  through  which  the  line  is  to  be  drawn  have  been 


FIG.  259.    USING  THE  IRREGULAR  CURVE 


located,  proceed  to  draw  the  line  as  follows,  referring  to  Fig. 
259  as  an  example.  Beginning  at  the  left  end  of  the  line,  find 
by  trial  that  portion  of  the  irregular  curve  which  will  fit  as 

225 


226  MECHANICAL  DRAWING 

many  consecutive  points  as  possible.  To  secure  a  smooth  curve 
the  line  drawn  should  not  go  through  all  of  the  points  coinci- 
dent with  the  irregular  curve.  Example,  Fig.  259.  If  the 
irregular  curve  coincides  with  the  line  for  the  distance  A  only 
the  distance  B  should  be  drawn  with  this  setting  of  the  curve. 
In  setting  the  irregular  curve  after  a  section  has  been  drawn 
care  should  be  taken  to  fit  it  back  on  a  portion  of  the  line 
already  drawn  to  insure  a  smooth  joint.  Example:  C,  the  new 
setting,  overlaps  B,  previously  drawn.  The  irregular  curve 
should  always  be  between  the  draftsman  and  the  line  being 
drawn.  The  forearm  should  be  nearly  perpendicular  to  the 
tangent  to  the  curve  at  any  point. 

When  inking  a  curve  the  pen  should  be  held  vertically  and 
rotated  on  its  axis  as  the  line  is  drawn  to  keep  the  nibs  always 
in  the  direction  of  the  edge  of  the  irregular  curve. 


FIG.  260.     CONSTRUCTING  ANGLES  OF  5°,  10°,  ETC. 

Constructing  Angles  in  Multiples  of  5°.  Angles  of  5°  or 
10°  are  easily  constructed,  as  shown  in  Fig.  260.  With  the 
T-square  and  triangle  two  lines  are  drawn  at  30°  to  each  other. 
With  their  intersection  as  a  center  draw  an  arc  of  any  con- 
venient radius.  With  the  dividers  trisect  the  arc  between  the 
two  lines.  Radial  lines  through  these  points  on  the  arc  are 
10°  apart. 

An  angle  of  5°  may  be  obtained  by  trisecting  an  arc  between 
two  lines  making  an  angle  of  15°  with  each  other,  or  bisecting 
an  arc  between  two  lines  making  an  angle  of  10°  with  each 
other. 

The  use  of  a  protractor  affords  a  more  direct  method  of 
constructing  angles. 

DATA  FOE  PLATE  24 

Given:  A  cam,  Fig.  261;  a  swivel  hook,  Fig.  262;  and  a 
swing  arm,  Fig.  263. 


ADVANCED  DRAWING 


227 


Required:  To  make  a  pencil  mechanical  drawing  of  the 
object  shown  in  Fig.  261,  262,  or  263,  as  assigned  by  the 
instructor. 

Instructions:  Use  the  inclined  lower  case  letters  for  notes 
and  the  inclined  Arabic  numerals  for  dimensions  on  this  draw- 
ing. The  title  should  be  lettered  in  vertical  capital  letters. 


As  shown  pattern 
Rererse  pattern  #//7/6  ft 

FIG.  261.    OPERATING  CAM  FOR  24"  PIVOTED  BUCKET  CONVEYOR 
EIGHT  WANTED  —  CAST  IRON 


The  points  for  the  curve  of  the  cam  are  determined 
by  measuring  from  the  center  of  the  hub  on  radial  lines  10° 
apart.  To  obtain  dimensions  for  calculating  the  size  of  the 
enclosing  rectangle,  construct  a  few  points  of  the  curve  and 
scale  the  layout. 

Swivel  Hook.     The  drawing  of  the  swivel  hook  is  peculiar 
in  that  only  one  view  is  given.    A  second  view  is  made  unneces- 


228 


MECHANICAL  DRAWING 


sary  in  this  case  by  the  revolved  section  and  the  evident  form 
of  the  swivel  end. 


1 


FIG.  262. 


SWIVEL  HOOK  FOR  -TON  ELECTRIC  CRANE 
ONE  WANTED — STEEL 

(All  dimensions  in  inches.) 


10 


Lbs. 


250 

500 

1000 

2000 

3000 

4000 

6000 

8000 

10000 

12000 

16000 

20000 


tt 


tt 

iA 

ill 
U 

m 


2M 


1A 
If 
14 
if 

2 
2! 


H 


1A 
ill 

ill 


34 


H 


2ff 
3 


G 


ff 
ft 

IA 
14 

ift 

2M 


3ft 


H 


II 

li 
tt 

111 

IA 


iA 

if 

2M2 

2M 

31 

Hi 


if 
iA 

U 


K 


ft 

1A 
I A 

if 
i  A 

H 

21 

2I-6 


IA 

if 

IA 

14 

itt 


2H 


4H 


M 


44 


H 


14 
U 
i  A 
if 


i-A 
1H 
ill 
itt 
1ft 


0 


A 

§ 

tt 

f 

IA 
11 

if 

2 

2f 

2f 

3| 

41 


II 
tt 
tt 

if 

i& 
i-H- 


Q 

Hi 
if 

itt 

21 
2H 


tft 

2£4& 

2| 

2f 


R 

Itt 
If 
Itt 
21 


4H 
51 


ADVANCED  DRAWING 


229 


A  table  of  values  of  the  dimension  symbols  for  various  sizes 
of  the  hook  is  given  with  the  view.  This  is  called  a  tabulated 
drawing. 

Swing  Arm.  Attention  is  called  to  the  method  of  showing 
the  detail  of  the  fork  by  means  of  a  partial  auxiliary  view; 
also  to  the  method  of  relating  centers  by  coordinate  dimensions. 


FIG.  263. 


SWING  ARM  FOR  OHIO  MONARCH  SHREDDER 
ONE  WANTED-^CAST  IRON 


DATA  FOR  PLATE  25 

Given :     The  pencil  mechanical  drawing,  Plate  24. 
Required:     To  make  a  tracing  of  Plate  24. 
Instructions:   The  lines  of  the  drawing  should  be  inked  in 
the  following  order: 

1.  Arcs  and  circles. 

2.  Irregular  curves. 

3.  Horizontal  lines. 

4.  Vertical  lines. 

5.  Inclined  lines. 


230  MECHANICAL  DRAWING 

SKETCHING  FROM  THE  OBJECT 

PREPARATORY  INSTRUCTIONS  FOR  PLATE  26 

Freehand  sketches  may  be  made  by  a  designer  to  get  an  idea 
of  the  form  of  certain  parts  in  working  out  his  design.  A 
designer  or  chief  draftsman  may  use  them  as  a  means  of  con- 
veying his  ideas  to  a  junior  draftsman. 

In  case  a  machine  is  broken  time  may  often  be  saved  by 
sketching  the  broken  parts  in  the  shop  and  having  parts  made 
to  replace  them  instead  of  sending  to  the  manufacturer  of  the 
machine  for  repairs.  When  a  change  of  design  is  contemplated 
and  the  original  drawings  are  not  to  be  had,  sketches  of  the 
parts  affected  may  be  made  from  the  existing  machine  and  the 
desired  changes  incorporated  in  the  mechanical  drawing  made 
from  sketches.  When  time  permits  and  it  is  desirable  to  have 
a  permanent  record  of  the  drawing  a  mechanical  drawing  should 
be  made  from  the  sketch,  but  in  an  emergency  the  sketch  if 
carefully  drawn  and  checked  may  be  used  as  a  shop  drawing. 

In  making  the  orthographic  sketches  of  Chapter  II,  the 
fact  that  certain  views  of  the  object  were  shown  in  correct 
proportion  and  were  dimensioned  made  the  task  of  drawing  the 
other  views  of  the  object  to  larger  scale  a  simple  process. 

The  drawing  of  orthographic  sketches  from  dimensioned  per- 
spective sketches,  Chapter  III,  increased  the  difficulty  of  select- 
ing and  arranging  the  views  and  to  some  extent  the  dimensions. 

Compared  to  sketching  from  orthographic  and  perspective 
views  the  average  beginner  will  find  the  making  of  an  ortho- 
graphic sketch  from  the  object  a  rather  intangible  problem. 
He  will  find  it  difficult  to  represent  in  outline  an  object  which 
to  the  eye  stands  out  in  relief  in  light  and  shadow.  At  the 
same  time  he  must  keep  in  mind  the  fact  that  only  two  dimen- 
sions can  be  represented  in  each  view.  He  is,  also,  confronted 
with  the  necessity  of  establishing  center  lines,  datum  lines,  etc., 
which  are  not  edges  of  the  object  but  are  of  prime  importance 
in  the  drawing. 

He  must  select  dimensions  to  show  the  proper  relation 
between  the  details  of  the  object.  These  dimensions  must  also 


ADVANCED  DRAWING  231 

be  selected  to  show  similar  distances  on  parts  which  are  fitted 
to  the  object.  He  must  use  his  judgment  as  to  the  accuracy 
with  which  each  measurement  should  be  made,  as  to  the  allow- 
ance for  inaccuracies  of  workmanship,  inaccuracies  inherent  in 
the  process  of  manufacture,  etc. 

Selecting  Views.  In  selecting  the  views  of  an  object  to  be 
drawn  the  principles  developed  in  previous  chapters  should  be 
used.  In  general  only  necessary  views  are  drawn,  but  in  the 
sketch  additional  views,  partial  views,  sections,  etc.,  may  be 
drawn  in  preference  to  complicating  the  necessary  views  with 
lines. 

Methods  Used  in  Drawing.  After  an  inspection  of  the  object 
and  after  a  decision  has  been  reached  as  to  what  views  are  to  be 
drawn,  the  student  should  place  the  object,  if  it  is  removable, 
so  that  he  can  obtain  the  required  views  without  changing  its 
position.  Very  often  the  shifting  of  the  object  leads  to  errors 
in  the  relative  position  of  the  views,  such  as  placing  the  left 
side  view  to  the  right  instead  of  to  the  left  of  the  front  view. 
With  the  object  always  in  the  same  position  and  the  principles 
as  to  relation  of  views,  developed  in  former  chapters,  well  in 
mind,  such  errors  are  not  likely  to  occur.  The  views  should 
show  the  object  in  as  good  proportion  as  can  be  obtained  without 
scaling  it.  Time  should  not  be  wasted  in  taking  dimensions 
at  this  stage  and  attempting  to  lay  them  out  to  scale. 

The  first  step  in  the  construction  of  the  drawing  is  to  locate 
center  or  other  reference  lines.  Circles  should  be  constructed 
by  first  drawing  two  center  lines  at  right  angles.  The  radii 
should  then  be  estimated  from  the  intersection  on  these  lines, 
and  the  circle  drawn  through  the  four  points  located. 

If  the  object  is  of  cylindrical  form  it  will  usually  be  found 
advantageous  to  draw  the  circular  view  first  because  of  the 
ease  with  which  the  other  views  may  be  drawn  by  projecting 
the  diameters  from  the  circular  view.  In  some  cases  where  the 
views  of  the  details  of  the  object  are  interdependent  it  will  be 
necessary  to  construct  two  or  more  views  simultaneously. 

The  use  of  the  coordinate  paper  greatly  facilitates  the  align- 
ment and  proportioning  of  the  details  in  different  views.  The 
student  should  learn  to  use  the  ruled  lines  merely  as  a  guide 


232  MECHANICAL  DRAWING 

in  locating  and  proportioning  the  views.  The  use  of  the  squares 
as  units  of  measurement  for  the  purpose  of  drawing  the  object 
to  scale  is  not  to  be  considered ;  for  while  it  is  admitted  that 
their  use  will  aid  in  proportioning  the  drawing,  it  is  not  one  of 
the  functions  of  a  freehand  sketch  to  show  the  object  in  accurate 
proportion,  and  the  counting  of  the  squares  entails  a  serious 
waste  of  time. 

Selection  and  Arrangement  of  Dimensions.  When  the  views 
of  the  object  are  complete  and  have  been  checked  carefully  to 
make  sure  that  they,  together  with  necessary  supplementary 
notes,  fully  represent  the  object,  the  question  of  dimensioning 
should  next  be  considered. 

To  dimension  an  object  properly  the  draftsman  must  have 
some  knowledge  of  the  process  through  which  it  must  go  in  the 
shop  to  become  a  finished  product.  If  it  be  a  casting  he  must 
know  what  dimensions  the  patternmakers  will  use  in  making 
the  pattern;  if  it  has  finished  surfaces  he  must  know  with 
what  machines  each  is  finished  and  give  the  dimensions  in  such 
a  way  that  the  machinist  may  use  them  directly.  Example : 
The  diameter  of  a  part  to  be  turned  in  the  lathe  should  be  given 
rather  than  the  radius,  since  the  most  convenient  and  accurate 
method  of  measuring  a  cylindrical  surface  is  by  means  of  the 
caliper  or  micrometer. 

Enough  dimensions  should  be  given  to  determine  completely 
the  sizes  and  relation  of  the  details  of  the  object.  When  a 
sketch  is  made  at  some  distance  from  the  place  at  which  it  is 
to  be  used  either  to  furnish  information  for  a  mechanical  draw- 
ing or  as  a  shop  drawing,  the  draftsman  must  be  sure  that  all 
necessary  dimensions  are  given.  However,  he  should  guard 
against  giving  unnecessary  or  useless  dimensions  in  an  attempt 
to  avoid  omitting  necessary  dimensions.  All  finished  surfaces, 
special  fits,  etc.,  should  be  marked  in  such  a  way  that  they 
cannot  be  misunderstood.  The  nature  of  the  sketch  admits 
of  a  freer  use  of  explanatory  notes  than  would  be  tolerated  on 
the  mechanical  drawing. 

Details  which  are  required  to  be  accurately  located  on  the 
object  should  be  referred  by  dimensions  to  center  lines  or  fin- 
ished surfaces.  As  the  dimensions  to  be  given  are  planned  the 


ADVANCED  DRAWING 


233 


extension  and  dimension  lines  should  be  drawn,  but  the  dimen- 
sion figures  should  not  be  inserted  until  all  such  lines  are  drawn. 
When   the   extension   and   dimension   lines   are    drawn   the 
arrowheads  should  be  made. 


MEASUREMENTS 
MEASURING  INSTRUMENTS 

The  following  paragraphs  contain  a  short  description  of  the 
more  common  tools  used  in  taking  measurements  from  the  object 
for  the  purpose  of  dimensioning  a  sketch : 


FIG.  264.    FOLDING  RULE 


The  Folding  Rule.    Rules  are  made  of  various  lengths  which 
may  be  folded  and  carried  in  the  pocket.    The  smallest  divisions 


are  usually  TV'  and 


Their  construction  makes  the  division 


into  smaller  fractions  of  an  inch  unwarrantable  as  these  rules 


FIG.  265.     STEEL  TAPE 


cannot  be  depended  upon  to  read  accurately  to  smaller  units. 
A  two-foot  rule  will  be  found  very  serviceable  where  accuracy 
is  not  required.  While  convenient  in  measuring  long  distances 
they  are  in  general  suitable  only  for  rough  work.  Fig.  264. 


234 


MECHANICAL  DRAWING 


The  Steel  Tape.  Steel  tape  may  be  had  in  lengths  of  3  feet  to 
200  feet  or  more.  As  in  the  case  of  the  rules  their  divisions  are 
coarse  and  cannot  be  used  for  accurate  measurements.  Fig.  265, 


FIG.  266.    ADJUSTABLE  SQUARE 

The  Steel  Scale.  For  accurate  measurements  steel  scales  are 
used.  These  scales  may  be  had  in  lengths  of  1"  to  72",  and  with 
various  combinations  of  graduations  on  the  two  edges  of  each 


FIG.  267.     OUTSIDE  CALIPER.     INSIDE  CALIPER 


side. 


The  most  common  graduations  are  J">  iV?  sV>  75  V> 
ifo".    Fig.  266. 

The  Adjustable  Square.  Fig.  266  shows  a  square  in  which 
the  blade  is  adjustable  in  the  stock.  The  blade  is  an  ordinary 
steel  scale  with  a  groove  made  to  receive  a  hook  which  serves 


ADVANCED  DRAWING  235 

to  clamp  the  blade  in  the  stock.  The  stock  is  furnished  with 
a  level.  This  instrument  will  be  found  useful  in  many  ways. 

Calipers.  Calipers  are  used  for  obtaining  measurements  of 
length  or  diameter  where  the  scale  cannot  be  applied  directly. 
After  they  are  set  to  the  distance  which  is  to  be  measured  they 
are  placed  upon  a  scale  and  the  distance  read.  Fig.  267  shows 
two  forms  of  calipers,  one  adapted  to  outside  measurements, 
such  as  diameters  of  shafts,  etc.,  while  the  other  is  best  suited 
to  inside  measurements,  such  as  the  diameter  of  holes. 

Other  Devices,  such  as  the  plumb  bob,  straight  edge,  and 
surface  gauge,  may  be  of  occasional  use  in  taking  measurements 
from  the  object. 

TAKING  MEASUREMENTS 

Having  drawn  the  dimension  lines,  extension  lines,  and 
arrowheads,  there  remains  the  taking  of  dimensions  from  the 
object  and  inserting  them  on  the  drawing.  In  doing  this  judg- 
ment must  be  exercised  in  determining  with  what  degree  of  ac- 
curacy each  measurement  should  be  taken.  Examples :  Dimen- 
sions between  rough  surfaces  usually  need  not  be  given  closer 
than  the  nearest  iV'  or  ^",  while  the  inside  diameter  of  the 
bushing  in  which  a  shaft  is  to  run  would  probably  be  given 
.003"  or  .004"  larger  than  the  diameter  of  the  shaft. 

Judgment  must  also  be  exercised  in  determining  whether 
irregularities  such  as  the  uneven  thickness  of  castings,  lack  of 
symmetry,  apparent  discrepancies  in  spacing  of  holes,  etc.,  are 
intentional  and  essential  to  the  design  and  construction  of  the 
object,  or  whether  they  are  non-essentials  which  have  come  about 
through  natural  causes  in  the  process  of  manufacture  or  poor 
workmanship,  and  should  be  eliminated  from  the  drawing. 

The  problems  arising  in  the  taking  of  measurements  from 
the  object  are  so  varied  that  no  attempt  will  be  made  here  to 
discuss  the  subject  fully.  However,  a  few  examples  may  be 
given  which  will  illustrate  the  use  of  the  measuring  instruments 
and  also  the  general  principles  involved  in  securing  dimensions. 

The  distance  between  points  on  the  same  plane  surface  such 
as  the  distance  between  two  parallel  edges  of  the  surface  and 


MECHANICAL  DRAWING 


FIG.  268.     MEASURING  A  LINEAR  DISTANCE  WITH  THE  SCALE 


FIG.  269.    MEASURING  LINEAR  DISTANCES  WITH  SQUARE 

the  length  of  cylinders  may  be  measured  directly  with  the  rule 
or  steel  scale,  as  shown  in  Fig.  268.  This  method  is  only  applica- 
ble for  accurate  measurement  when  the  corners  are  sharp.  When 
the  corners  are  rounded  che  same  dimension  may  be  obtained 
by  using  the  square  or  caliper,  as  shown  in  Fig.  269  or  270. 


ADVANCED  DRAWING 


237 


The  use  of  the  square  here  needs  no  explanation.  The  caliper 
must  be  set  yery  carefully  so  that  its  points  touch  both  surfaces 
between  which  the  distance  is  to  be  measured,  but  not  with 
enough  pressure  to  spring  the  caliper.  The  proper  adjustment 


FIG.  270.     MEASURING  LINEAR  DISTANCES 
WITH  THE  CALIPER 


FIG.  271.    READING  THE  CALIPER  MEASUREMENT  FROM  THE  SCALE 

is  obtained  by  means  of  the  thumb  screw  on  the  adjustable  cali- 
per or  by  tapping  the  leg  against  a  solid  object  in  the  case  of 
the  plain  caliper.  The  distance  between  the  points  of  the  caliper 


238 


MECHANICAL  DRAWING 


is  measured  with  the  steel  scale,  as  shown  in  Fig.  271.  Note 
that  one  point  of  the  caliper  rests  against  the  end  of  the  scale 
so  that  the  operator's  attention  may  be  given  entirely  to  reading 
the  scale  division  at  the  other  point. 

The  outside  caliper  is  used  in  obtaining  dimensions  of  curved 
surfaces.     See  Fig.  272.     It  is  adjusted  and  the  measurement 


FIG.  272.     MEASURING  THE  DIAMETER 
OF  A  CYLINDER  WITH  THE  CALIPER 


taken  from  the  scale  as  previously  described. 

The  inside  caliper  is  used  in  measuring  the  diameters  of 
holes  and  the  openings  between  surfaces  where  the  scale  cannot 
be  applied.  Fig.  273.  Measurements  are  obtained  from  the 


FIG.  273. 

MEASURING  THE  DIAMETER  OF  A 
HOLE  WITH  THE  INSIDE  CALIPER 

inside  caliper  by  placing  it  over  the  scale,  as  shown  in  Fig.  274. 
Note  that  the  scale  is  placed  against  a  smooth  surface  and  at 
right  angles  to  it.  One  point  of  the  inside  caliper  is  placed 
against  the  smooth  surface.  By  this  method  the  scale  division 
opposite  the  other  point  may  be  easily  and  accurately  read. 
When,  as  is  very  often  the  case,  it  is  necessary  to  locate 


ADVANCED  DRAWING 

centers  of  holes  with  reference  to  each  other  or  with  reference 
to  some  finished  surface  or  datum  line,  a  difficulty  arises  from 


FIG.  274.     READING  MEASUREMENTS  FROM  THE  INSIDE  CALIPER 

the  fact  that  a  center  line  does  not  exist  on  the  object  and  must 
be  established  or  the  dimension  obtained  in  a  roundabout  way. 


FIG.  275.    MEASURING  THE  CENTER  TO  CENTER  DISTANCE  OF  EQUAL  HOLES 


In  the  case  of  two  holes  of  equal  diameter  the  center-to- 
center  distance  may  be  obtained  by  measuring  from  the  near 
edge  of  one  to  the  far  edge  of  the  other.  Fig.  275.  The  center- 
to-center  distance  of  holes  of  unequal  diameter  may  be  obtained 


240 


MECHANICAL  DRAWING 


by  measuring  from  the  near  edge  of  one  to  the  near  edge  of  the 
other  and  adding  one-half  the  diameter  of  each.  The  distance 
from  an  edge  or  surface  to  the  center  of  a  hole  may  be  had  by 
adding  one-half  the  diameter  of  the  hole  to  the  distance  from 
the  edge  or  surface  to  the  near  edge  of  the  hole.. 

Fig.  275  shows  an  object  the  form  of  which  makes  it  neces- 
sary to  use  the  caliper  in  measuring  the  distance  between  the 
centers  of  the  two  holes.  The  corners  of  cast  parts  are  usually 


FIG.   276.     TYPE  PROBLEM — CYLINDER   HEAD. — FREEHAND   SKETCH 

rounded  or  filleted.  The  radii  of  these  curves  are  not  easily 
measured,  but  usually  it  is  unnecessary  to  measure  them  accu- 
rately. The  radii  of  small  fillets  may  often  be  estimated  entirely 
by  eye  or  the  scale  held  against  the  object  at  one  point  of 
tangency  and  the  radius  estimated  by  placing  the  thumb  nail 
at  the  division  on  the  scale  opposite  the  other  tangent  point. 
A  very  satisfactory  method  applicable  in  some  cases  is  to  place 
the  object  over  a  sheet  of  paper  and  trace  around  the  corner 
or  fillet  with  a  sharp  pencil.  The  center  of  the  arc  thus  obtained 
may  be  found  by  trial  with  the  dividers  and  the  radius  measured. 


ADVANCED  DRAWING 


241 


Checking.  Where  a  number  of  detail  dimensions  have  been 
taken  which  make  up  the  length  of  a  larger  detail  or  the  whole 
length  of  the  object,  this  over-all  dimension  should  be  checked 
by  direct  measurement  as  well  as  by  addition  of  the  detail 
dimensions. 


FIG.  277.    TYPICAL  OBJECTS  FOR  FIRST  DRAWING  FROM  MODEL 
DATA  FOR  PLATE  26 

Given :     A  simple  machine  part  or  model  preferably  finished 
all  over.    Fig.  277  shows  typical  objects  for  this  plate. 

Required:     To  make  a  freehand  orthographic  sketch. 

Instructions:  The  following  is  a  brief  summary  of  the  steps 
arranged  in  sequential  order  to  be  taken  in  making  a  sketch 
from  the  object.  It  is  believed  that  by  carefully  observing  the 
steps  of  this  outline  the  draftsman  will  be  able  to  make  the 
sketch  complete  and  accurate  with  a  minimum  amount  of 
effort,  and  to  do  the  work  in  the  least  amount  of  time. 
•1.  Select  views. 

2.  Draw   views    (proportioning    details   by   eye   without 
taking  dimensions). 

3.  Plan  dimensions — draw  dimension  and  extension  lines. 

4.  Draw  arrowheads. 

5.  Take  dimensions  from  the  object  and  place  figures. 

6.  Mark  finished  surfaces. 

7.  Print  all  notes,  including  the  name  of  the  part  drawn, 
the  number  required,  and  the  material  from  which  each 
part  is  to  be  made. 


242  MECHANICAL  DRAWING 

DATA  FOR  PLATE  27 

Given:     The  orthographic  sketch,  Plate  26. 

Required:     To  make  a  mechanical  drawing  from  Plate  26. 

DATA  FOR  PLATE  28 

Given:     The  mechanical  drawing,  Plate  27. 
Required:     To  make  tracing  from  Plate  27. 


FIG.  278.     TYPICAL  MODEL  OF  COMPLETE  MACHINE 

PREPARATORY  INSTRUCTIONS  FOR  PLATE  29 

The  model  for  this  plate  should  be  a  complete  machine  or 
some  unit  of  a  machine  which  is  composed  of  several  parts.     The 


ADVANCED  DRAWING 


243 


parts  of  the  model  then  can  be  divided  into  several  groups  and 
each  group  assigned  to  a  student.*  Fig.  278  shows  a  typical 
model,  the  parts  of  which  are  divided  into  groups.  Fig.  279. 
The  detail  drawings  of  this  model  will  be  used  later  (Plate  35) 
in  making  an  assembly  drawing. 

DATA  FOR  PLATE  29 

Given :     A  part  or  group  of  parts  of  a  machine. 
Required:     To  make  an  orthographic  sketch  of  each  part 
assigned  by  the  instructor. 


FIG.  279.    SHOWING  GROUPING  OF  PARTS  OF  MACHINE  FOR  ASSIGNMENT 


Instructions:  In  making  the  sketches  proceed  according  to 
the  steps  outlined  for  Plate  25. 

More  than  one  part  may  be  drawn  on  each  sheet,  provided 
the  views  are  not  too  small  or  crowded  too  closely  together. 

In  drawing  and  dimensioning  these  objects  the  student 
should  check  each  detail  with  the  parts  which  are  related  to  it 
or  depend  upon  it  in  any  way. 

Note  should  be  made  of  the  name  of  each  part,  the  number 
required,  and  the  material  from  which  it  is  made. 


*  This   plan   gives  best   results  when   there   are   from   3    to   6   students 
working  on  each  model. 


244  MECHANICAL  DRAWING 

PEEPAEATOEY  INSTRUCTIONS  FOE  PLATE  30 

When  making  the  mechanical  drawing  all  of  the  parts  in 
each  group  should  be  drawn  on  one  sheet  if  possible.  The  ar- 
rangement of  the  views  should  be  such  as  to  make  the  best  use 
of  the  space  available,  and  at  the  same  time  produce  a  pleasing 
effect  for  the  sheet  as  a  whole.  This  will  require  careful  study. 
The  solution  will  depend  largely  on  the  draftsman's  judgment. 
In  general  it  may  be  said  th#t  the  distance  between  views  of 
different  objects  should  be  greater  than  that  between  views  of 
the  same  object.  The  enclosing  rectangles  for  each  view  may 
be  drawn  lightly  to  make  sure  that  sufficient  space  has  been 
allowed  for  the  drawing  of  all  parts  before  drawing  the  views, 
or  better  yet  a  rectangle  equal  in  size  to  the  enclosing  rectangle 
for  the  views  of  each  part  may  be  cut  from  paper  and  moved 
about  until  the  best  possible  arrangement  is  secured. 

Before  starting  to  plan  the  arrangement  of  the  sheet  the 
areas  occupied  by  the  bill  of  material  and  the  title  block  should 
be  laid  out.  The  bill  of  material  as  shown  in  Fig.  282  contains 
the  reference  figure  corresponding  to  the  one  placed  near  the 
views  of  the  object,  the  name  of  the  object,  the  number  required, 
and  the  materials  from  which  it  is  made.  The  width  of  the  bill 
of  material  is  equal  to  the  width  of  the  title  block  and  the  height 
depends  upon  the  number  of  parts  to  be  listed.  See  Fig.  147 
for  detail  dimensions. 

In  some  shops  the  information  referred  to  above  is  given  for 
each  part  near  the  views  of  that  part  and  is  called  a  sub-title. 

The  title  for  a  sheet  containing  the  drawings  of  several  parts 
must  be  a  general  one  in  which  the  word  "details"  usually 
takes  the  place  of  the  name  of  the  part  drawn.  See  Fig.  280. 
It  is  often  convenient  to  use  different  scales  for  the  various 
objects,  in  which  case  the  scale  for  each  should  be  printed  with 
the  views  of  that  part  and  the  words,  ' '  Scales  as  noted, ' '  printed 
in  the  usual  place  in  the  title. 

DATA  FOE  PLATE  30 

Given:     The  orthographic  sketch,  Plate  29. 

Required:     To  make  a  mechanical  drawing  from  Plate  29. 


246  MECHANICAL  DRAWING 

DATA  FOE  PLATE  31 

Given :     The  pencil  mechanical  drawing,  Plate  30. 

Required:     To  make  a  tracing  of  Plate  30. 

Instructions:  The  width  of  the  top  and  left  sides  of  the  rec- 
tangle enclosing  the  bill  of  material  and  the  vertical  division 
.lines  should  be  object  line  width  (^  ").  The  horizontal  lines 
between  lines  of  lettering  should  be  center  line  width  d^g"). 

PREPARATORY  INSTRUCTIONS  FOR  PLATE  32 

One  of  the  problems  of  the  draftsman  is  to  make  detail  draw- 
ings from  the  original  layout  of  a  machine  in  which  the  parts 
are  shown  assembled.  On  this  assembly  drawing  some  impor- 
tant dimensions  may  be  given,  others  may  be  scaled  from  the 
drawing,  and  the  remainder  must  be  supplied  by  the  draftsman 
himself.  Since  this  course  does  not  presuppose  a  knowledge  of 
design  all  necessary  dimensions  will  be  given  on  the  assembly 
drawing  from  which  the  student  draws  this  plate. 

The  reading  of  the  assembly  drawing  to  get  the  correct  form 
for  each  detail  will  in  most  cases  require  careful  study.  The 
different  parts  may  be  distinguished  when  in  section  by  various 
crosshatching  for  different  metals  and  by  the  sectioning  of  adja- 
cent parts  at  opposite  angles.  But  even  with  this  aid  the  differ- 
ent views  must  be  compared  carefully  to  check  the  first  impres- 
sion gained  of  the  form  of  each  part  and  to  make  sure  that  no 
detail  has  been  overlooked.  Each  part  of  the  object  must  be 
dimensioned  completely.  It  is  not  sufficient  to  give  a  dimension 
on  the  views  of  one  part  and  omit  the  same  dimension  on  the 
views  of  another  part,  even  though  it  is  evident  that  the  dimen- 
sion is  the  same  on  both. 

DATA  FOR  PLATE  32 

Given :  An  assembly  drawing  of  an  adjustable  step  bearing, 
Fig.  283,  a  connecting  rod  end,  Fig.  284,  and  a  pipe  union, 
Fig.  285. 

Required:  To  make  a  freehand  orthographic  detail  sketch 
of  the  object  shown  in  Fig.  283,  284,  or  285  as  assigned  by  the 
instructor. 


ADVANCED  DRAWING 


247 


FIG.  281.     TYPE  PROBLEM — JACK  SCREW. — ASSEMBLY  DRAWING 


ADVANCED  DRAWING 


249 


Adjustable  Step  Bearing.  The  step  bearing  is  used  to  sup- 
port a  vertical  shaft.  Its  parts  as  designated  by  the  figures  in 
circles  in  Fig.  283  are  named  as  follows: 

1.  Base.  4.  Lower  bearing  disc. 

2.  Bearing  cup.  5.  Set  screw. 

3.  Upper  bearing  disc.     6.  Lock  nut. 

7.  Bushing. 


SECTION  ,ON   ABC 
FIG.  283.    ADJUSTABLE  STEP  BEARING 


250 


MECHANICAL  DRAWING 


It  should  be  noted  that  the  lower  end  of  (2)  is  spherical 
and  that  (2)  is  adjusted  in  (1)  by  means  of  set  screws  (5), 
acting  against  three  of  its  faces.  The  intersections  of  the 
spherical  surfaces  with  these  faces  result  in  curves  correspond- 
ing to  the  chamfer  curves  of  the  hexagonal  head  cap  screw. 


6  Notches  f'mde,  j-'eleep 


FIG.  284.    CONNECTING  KOD  END  FOR  NORDBERG  CORLISS  ENGINE 

Connecting  Rod  End.  This  is  the  crank  end  of  a  connect- 
ing rod  for  a  compound  Corliss  engine.  Its  parts  as  designated 
by  the  figures  in  circles  in  Fig.  284  are  named  as  follows : 

1.  Rod  end.  4.  Retaining  nut. 

2.  Stationary  box.  5.  Adjusting  wedge, 

3.  Adjustable  box.  6.  Cap  screw. 

7.  Washer/ 


ADVANCED  DRAWING 


251 


Provision  is  made  for  taking  up  wear  on  the  box  and  crank 
pin  by  moving  the  adjustable  box  toward  the  center  of  the  pin. 
This  is  accomplished  by  loosening  the  upper  cap  screw  and 


(All  dimensions  in  inches.) 


A 

B 

C 

D 

E 

F 

G 

H 

I 

J 

K 

1 

1.246 

1.048 

.198 

1.74 

1.79 

1.98 

2.01 

2.13 

2.19 

2.49 

4 

1.592 

1.380 

.212 

2.12 

2.18 

2.37 

2.40 

2.52 

2.58 

2.90 

if 

1.831 

1.610 

.221 

2.40 

2.46 

2.66 

2.69 

2.81 

2.87 

3.20 

2 

2.301 

2.067 

.239 

2.89 

2.95 

3.16 

3.19 

3.31 

3.38 

3.74 

^ 

2.775 

2.468 

.307 

3.39 

3.45 

3.67 

3.70 

3.86 

3.93 

4.39 

L 

M 

N 

O 

P 

Q 

.R 

S 

T 

U 

V 

X 

.49 

A 

11 

.3625 

.15 

1.003 

H 

1.565 

1.76 

.007 

.10 

1.315 

.53 

.6 

11 

.3825 

.16 

1.073 

.9 

1.91 

2.15 

.007 

.11 

1.66 

.55 

.7 

11 

.4025 

.17 

1.123 

1.0 

2.18 

2.40 

.007 

.13 

1.9 

.60 

.8 

11 

.4225 

.18 

1.2025 

1.1 

2.66 

2.90 

.008 

.14 

2.375 

.77 

.9 

8 

.5225 

.23 

1.5225 

1.2 

3.16 

3.41 

.008 

.16 

2.875 

FIG.  285.    PIPE  UNION 


tightening  the  lower  one,  thus  drawing  down  the  wedge,  the 
inclined  surface  of  which  acts  against  a  similar  surface  on  the 
adjustable  box,  causing  it  to  move  toward  the  center  of  the 
bearing. 


252  MECHANICAL  DRAWING 

The  rod  is  finished  by  turning  in  the  lathe;  consequently 
any  section  at  right  angles  to  the  longitudinal  axis  is  circular 
in  outline.  The  front  and  back  faces  of  the  rod  are  plane.  The 
intersection  of  the  plane  surfaces  and  the  turned  surfaces  must 
be  represented  by  a  curve  in  the  front  view.  Points  on 
this  curve  may  be  found  by  taking  sections  at  intervals  and 
locating  the  points  where  the  circular  arcs,  cut  from  the  surface 
of  the  rod,  pierce  the  flat  faces.  An  example  of  the  construction 
is  shown  in  Fig.  284.  The  steps  in  the  construction  are  taken 
in  the  order  indicated  by  the  numbers. 

Pipe  Union.  Fig.  285  shows  a  union  for  joining  two  pieces 
of  pipe  to  facilitate  connection.  Its  parts  as  designated  by  the 
figures  in  circles  are  named  as  follows : 

1.  Swivel  end.  3.  Nut. 

2.  Screw  end.  4.  Gasket. 

The  dimensions  for  different  sizes  are  shown  in  the  table. 
The  values  of  A  are  nominal  inside  diameters.  It  will  be  noted 
that  the  actual  inside  diameters,  C,  differ  from  the  nominal 
diameters. 

In  making  the  drawing  the  decimals  given  in  the  table  should 
be  converted  to  the  nearest  one-thirty-second  or  one-sixty-fourth 
of  an  inch,  as  the  occasion  may  require,  by  referring  to  a  table 
of  decimal  equivalents. 

DATA  FOE  PLATE  33 

Given:     The  orthographic  sketch,  Plate  32. 
Required:     To  make   a   pencil  mechanical   drawing   from 
Plate  32. 

DATA  FOR  PLATE  34 

Given:     The  pencil  mechanical  drawing,  Plate  33. 
Required:     To  make  a  tracing  of  Plate  33. 

PEEPARATORY  INSTRUCTIONS  FOR  PLATE  35 

An  Assembly  or  General  Drawing  is  made  for  the  purpose  of 
showing  the  position  and  relation  of  parts  of  a  machine  or 
structure.  Usually  only  the  most  important  dimensions  are 
given.  Example :  Fig.  286. 


254  MECHANICAL  DRAWING 

DATA  FOE  PLATE  35 

Given:     Blueprints  for  all  of  the  parts  of  the  object  drawn 
in  Plates  29,  30,  and  31. 

Required:     To  make  a  pencil  mechanical  drawing  from  the 
details. 

DATA  FOR  PLATE  36 

Given:     The  pencil  mechanical  drawing,  Plate  35. 
Required:     To  make  a  tracing  of  Plate  35. 


CHAPTEE  IX 

AUXILIARY  VIEWS,  ISOMETRIC  AND  CABINET 
DRAWING,  TABLES,  ETC. 

Auxiliary  Views.  Views  of  an  object  other  than  those  com- 
monly used,  such  as  the  top,  front,  and  side  views,  are  some- 
times desirable.  Fig.  287  shows  an  object  in  which  a  part  is 


FIG.  287.     FRONT  AND  SIDE  VIEWS  OF  BRACKET 


inclined  to  the  horizontal.  The  side  view  is  difficult  to  draw. 
Dimensions  in  the  direction  of  the  axis  of  the  cylindrical  part 
do  not  show  in  their  true  size  in  this  view. 

255 


•  jSigL..   A 
By  eHiwing 


MECHANICAL  DRAWING 


By  Miwing  a  partferv^ew  of  the  object  looking  in  the  direc- 
tion of  the  axis  of  the  .inclined  pai^awid  another  partial  view 
looking  in  a  direction  at  right  anglelf  to  the  faces  of  the  flange 
on  this  part,  the  drawing  process  is  simplified  as  the  circles  and 
arcs  show  in  these  views  in  their  true  forms  and  sizes.  Fig.  288. 


FIG.  288. 


^REPRESENTATION  OF  BRACKET  SIMPLIFIED  BY  USE  OF 
AUXILIARY  VIEWS 


Isometric  Drawing  is  a  method  of  representing  objects  pic- 
torially.  While  an  isometric  drawing  does  not  give  a  true 
picture  of  the  object,  the  fact  that  measurements  are  made  and 
the  construction  laid  out  mechanically,  recommends  this  method 
of  representation  where  time  is  an  important  factor.  It  is  used 
often  in  patent  office  drawings  and  frequently  where  it  is  neces- 
sary to  show  the  form  of  an  object  to  one  who  is  not  accustomed 
to  reading  orthographic  drawing. 


AUXILIARY  VIEWS 


257 


Derivation  of  the  Axes.  To  get  an  understanding  of  the 
principles  'orKwhich  isometric  drawing  is  based,  consider  a  cube 
turned  into  a  position  so  that  one  of  its  diagonals  is  viewed 
endwise.  Fig.  289. 

\Vhen  in  this  position  the  three  edges  meeting  in  the  near 
corner  of  the  cube  are  represented  by  lines  120°  apart.  The 
120°  angles  represent  the  three  right  angles  around  the  corner 
of  the  cube.  Since  the  three  edges  forming  these  angles .  all 
make  the  same  angle  with  the  diagonal  of  the  cube  the  amount 
of  foreshortening  for  each  of  the  three  edges  is  the  same.  To 
determine  the  amount  of  foreshortening  to  draw  the  cube  full 
size  would  require  a  construction  or  a  special  scale.  But,  since 
the  three  edges  are  all  foreshortened  in  the  same  ratio,  the 


FIG.  289.     THE  CUBE  IN  ISOMETRIC. 

actual  length  of  the  edges  may  be  used  in  making  the  drawing. 
The  only  effect  of  this  will  be  to  increase  slightly  the  size  of  the 
drawing.  Fig.  289. 

The  three  lines  120°  apart  are  the  axes  parallel  to  which  all 
measurements  are  made  in  isometric  drawing. 

Non-Isometric  Lines.  A  line  which  is  not  parallel  to  one 
of  the  three  axes  is  a  non-isometric  line.  A  non-isometric  line 
is  drawn  by  referring  points  on  the  line  to  the  axes  by  means 
of  coordinates.  Fig.  290  shows  a  rectangular  solid  on  the  top 
face  of  which  is  a  non-isometric  line  consisting  of  a  curved  and  a 
straight  portion.  The  position  of  the  point  D  is  determined  in 
the  isometric  by  transferring  lengths  AB  and  AC  from  the 
orthographic  views  with  the  dividers  and  drawing  lines  BD 
and  CD  parallel  to  the  axes.  In  some  cases  where  a  figure 
containing  non-isometric  lines  is  to  be  drawn,  it  is  convenient 
to  enclose  the  figure  in  a  rectangle.  The  hexagon  in  the  side 


258 


MECHANICAL  DRAWING 


FIG.  290.     LOCATING  POINTS  ON  NON -ISOMETRIC  LINES  USING 
Two  COORDINATES 

face  of  the  rectangular  solid,  Fig.  290,  and  the  circle  enclosed 
in  a  square,  Fig.  290,  are  illustrations  of  this  point. 

When  non-isometric  lines  do  not  lie  in  a  face  of  a  rectangular 
solid  three  coordinates  are  necessary  to  locate  points  on  each 
line.  In  drawing  the  isometric  of  the  frustum  of  the  hexagonal 
pyramid,  Fig.  291,  the  base  is  first  enclosed  in  a  rectangle  and 


FIG.  291. 


LOCATING  POINTS  ON  NON-ISOMETRIC  LINES  USING 
THREE  COORDINATES 


AUXILIARY  VIEWS 


259 


the  points  on  the  top  face  are  located  by  three  coordinates  as 
shown.  The  lengths  AB,  BD,  and  DE  are  taken  from  the  ortho- 
graphic views  and  laid  off  on  the  isometric  in  the  directions 
parallel  to  the  three  axes. 

Isometric  Circle*.  Circles  may  be  drawn  by  locating  points 
as  described  above  or  by  the  four-center  method  shown  in  Fig. 
292.  Point  A,  the  center  for  the  smaller  arc,  is  located  by  lay- 


FIG.   292.     A  FOUR-CENTER  METHOD  FOR  DRAWING  CIRCLES  IN   ISOMETRIC 


•ing  off  AB  =  BC.  The  center  D  for  the  larger  arc  is  located 
by  drawing  AD  through  A  perpendicular  to  BE.  The  other 
centers  are  located  in  a  similar  manner.  The  arcs  are  tangent 
at  the  point  F.  The  four-center  method  is  an  approximation 
and  is  usually  suitable  only  for  full  circles.  Where  an  arc  is 
drawn  which  must  pass  through  certain  points  the  plotting 
method  is  preferable.  Fig.  293. 


260 


MECHANICAL  DRAWING 


FIG.  293.     METHODS  OF  DRAWING  CIRCLES  AND  ARC 

Cabinet  Drawing  is  similar  to  isometric  in  that  measure- 
ments are  made  parallel  to  three  axes.  One  of  the  axes  is  hori- 
zontal, the  second  vertical,  and  the  third  45°  to  the  horizontal. 
Fig.  294.  Actual  lengths  are  measured  parallel  to  the  hori- 
zontal and  vertical  axes  and  one-half  the  actual  lengths  are 
measured  parallel  to  the  45°  axis.  Any  figure  which  lies  in  a 
plane  parallel  to  the  plane  of  the  horizontal  and  vertical  axes 


FIG.  294.    CABINET  DRAWING  OF  CUBE 


AUXILIARY  VIEWS  261 

is  shown  in  its  true  size  and  shape.  For  example,  an  object 
which  has  a  number  of  circles  parallel  to  one  plane  is  more 
easily  represented  in  cabinet  than  in  isometric  drawing  since 


FIG.  295.    EXAMPLE  OF  AN  OBJECT  WITH  CIRCLES  AND  ARCS 
PARALLEL  TO  ONE  PLANE 

the  circles  can  be  drawn  with  the  compass.  Fig.  295.  However, 
when  a  circle  is  to  be  drawn  parallel  to  either  of  the  planes 
determined  by  the  45°  axis  and  the  horizontal  or  vertical  axis 
the  points  011  the  curve  must  be  plotted. 


262 


MECHANICAL  DRAWING 


TABLE  OF  DECIMAL  EQUIVALENTS  FKOM  Jj  TO  1  INCH 


Fraction 

Decimal  Equivalent 

Fraction 

; 

Decimal  Equivalent 

T2 

.015625 
03125 

H 

u 

.515625 
53125 

*>".r 

.046875 
0625 

ft 

A 

.546875 
5625 

A--- 

A  

~&:.. 

i  

078125 
.09375 
.  109375 
.125 

ft  ... 

tt"«.:: 

I  

.578125 
.  59375 
.609375 
.625 

*-::-;,,;yi 

A 

.  140625 
.  15625 
.  171875 
1875 

M...64... 
H 

H 

.640625 
.65625 
.671875 
6875 

**•• 

H... 
1-  

&...64... 

A  64-'' 
H 

.203125 
.21875 
.234375 
.25 
.265625 
.28125 
.296875 
.3125 
.328125 
34375 

#  ; 

•  4.--. 

It:. 

!  ';.-!! 
tf... 
ft  
ft 

H  
27  . 

703125 

.71875 
.734375 
.75 
.765625 
.78125 
.796875 
.8125 
.828125 
84375 

M... 
1 

.359375 
375 

32 

H 

.859375 
875 

H-. 

H... 

ft 

i  

.390625 
.40625 
.421875 
.4375 
.453125 
.46875 
.484375 
.5 

»-.-.-.,..!;; 

H  . 

H  
tt- 
ft  
H 

i  

.890625 
.90625 
.921875 
.9375 
.953125 
.96875 
984375 
1.00000 

AUXILIARY  VIEWS 


263 


TABLE  OF  DIMENSIONS  OF  U.  S.  STANDARD  BOLTS,  HEADS  AND 

NUTS,  ROUGH 

(All  dim  en  f  ions  in  inches.) 


DIAM. 

or 

BOLT 

NO.  or 

THDS. 
PER 
INCH 

SHORT  DIAMETER 
Or  HEXAGON 
OR  SQUARE 

LONG  DIAMETER 
Or  HEADS  AND 
NUTS 

THICKNESS 
HEXAGON  AND 
SQUARE 

DIAM. 

or 

TAP 
DRILL 
NEAREST 
64TH 

HOOT  DIAMETER 

Dist.  across  flats 

Hexagon 
Dist.  acr. 

Square 
corners 

Heads 

Nuts 

I 

20 

18 
16 

1 

1 

n 

H 

H 

¥ 

1 

i 

| 

\ 

.185 
.240 
.294 

14 

1 

4 

il 

If 

H 

.344 

49 

13 
12 
11 

j 

i 

i 

u 
if 

14 

1 

f 

i 

.400 
.454 
.507 

•; 

10 

9 

ij 

% 

18 

iff 

i 

1                A 

4                     < 

L 

4 

.620 
.731 

1 

8 

7 

H 
Itt 

« 

23 
3~2" 

2H 

II 

1 

H 

1 

.837 
.940 

7 

2 

&  \  5 

2M 

1 

1 

1.065 

6 
6 

21 

^ 

21  7 
TJ 

3M 

1A 

l 

i 

1.160 

1.284 

5    !        21 

3i^r 

3^4 

If 

1; 

M 

1.491 

t 

2 

44 

3i 

3fr 

1^ 

2 

II 

1.712 

2* 

44 

& 

4^ 

11 

21 

2 

1.962 

24 

4 

3 

4^1 

IT! 

24 

2aT 

2.176 

2f           4 

4 

4ff 

6^j 

2| 

2-| 

24f 

2.426 

3 

34 

4 

SH 

6H 

2A 

3 

2ii 

2.629 

i 

264 


MECHANICAL  DRAWING 


DIFFERENT  STANDARDS  OF  WIRE  GAUGES  IN  USE  IN 
THE  UNITED  STATES 

DIMENSIONS  IN  DECIMAL  PARTS  OF  AN  INCH 


NUMBER  OF 
WIRE 

GAUGE 

AMERICAN  OR 
BROWN 
&  SHARPE 

BIRMING- 
HAM OR 

STUB'S 

WIRE 

WASHBURN  A 
MOEN  MFG.  CO 
WORCESTER 

IMPERIAL 
WIRE 
GAUGE 

STUB'S 

STEEL 
WIRE 

u.  s. 

STANDARD 
FOR  PLATE 

MUSIC 
WIRE 

00000000 

.0083 

0000000 

0087 

000000 

.'464' 

!  46875 

.0095 

00000 

.432 

.4375 

.010 

0000 

.'46" 

^454 

.'3938 

.400 

.40625 

.011 

000 

.40964 

.425 

.3625 

.372 

.375 

.012 

00 

.3648 

.38 

.3310 

.348 

.34375 

.0133 

0 

.32486 

.34 

.3065 

.324 

.3125 

.0144 

1 

.2893 

.3 

.2830 

.300 

^227 

.28125 

.0156 

2 

.25763 

.284 

.2625 

.276 

.219 

.265625 

.0166 

3 

.22942 

.259 

.2437 

.252 

.212 

.25 

.0178 

4 

.20431 

.238 

.2253 

.232 

.207 

.234375 

0188 

5 

.18194 

.32 

.2070 

.212 

.204 

.21875 

.0202 

6 

.16202 

.203 

.1920 

.192 

.201 

.203125 

0215 

7 

.14428 

.18 

.1770 

.176 

.199 

.1875 

.023 

8 

.  12849 

.165 

.1620 

.160 

.197 

.171875 

.024 

9 

.11443 

.148 

.1483 

.144. 

.194 

.  15625 

.0253 

10 

.  10189 

.134 

.1350 

.128 

.191 

.140625 

0276 

11 

.090742 

.12 

.1205 

.116 

.188 

.125 

.028 

12 

.080808 

.109 

.1055 

.104 

.185 

.109375 

.0294 

13 

.071961 

.095 

.0915 

.092 

182 

.09375 

.0316 

14 

.064084 

.083 

.0800 

.080 

.180 

.078125 

.0324 

15 

.057068 

.072 

.0720 

.072 

.178 

.0703125 

.0346 

,   16 

.05082 

.065 

.0625 

.064 

.175 

.0625 

.0365 

17 

.045257 

.058 

.0540 

.056 

.172 

.05625 

.037 

18 

.040303 

.049 

.0475 

.048 

.168 

.05 

.0397 

19 

.03589 

.042 

.0410 

.040 

.164 

.04375 

.0415 

20 

.031961 

.035 

.0348 

.036 

.161 

.0375 

.0434 

21 

.028462 

.032 

.03175 

.032 

.157 

.034375 

.0464 

22 

.025347 

.028 

.0286 

.028 

.155 

.03125 

.048 

23 

.022571 

.025 

.0258 

.024 

.153 

.028125 

.0513 

24 

.0201 

.022 

.0230 

.022 

.151 

.025 

.0555 

25 

.0179 

.02 

.0204 

.020 

.148 

.021875 

.058 

26 

.01594 

.018 

.0181 

.018 

.146 

.01875 

.0626 

27 

.014195 

.016 

.0173' 

.0164 

.143 

.0171875 

.0656 

28 

.012641 

.014 

.0162 

.0149 

.139 

.015625 

.0728 

29 

.011257 

.013 

.0150 

.0136 

.134 

.0140625 

.076 

30 

.010025 

.012 

.0140 

.0124 

.127 

.0125 

.080 

31 

.008928 

.01 

.0132 

.0116 

.120 

.0109375 

.082 

32 

.00795 

.009 

.0128 

.0108 

.115 

.01015625 

.086 

33 

.00708 

.008 

.0118 

.0100 

.112 

.009375 

.090 

34 

.006304 

.007 

.0104 

.0092 

.110 

.00859375 

.095 

35 

.005614 

.005 

.0095 

.0084 

.108 

.0078125 

36 

.005 

.004 

.0090 

.0076 

.106 

.00703125 

.... 

37 

.004453 

.0068 

.103 

.006640625 

38 

.003965 

.0060 

.101 

.00625 

39 

.003531 

.0052 

.099 

.... 

40 

.003144 

.0048 

.097 



AUXILIARY  VIEWS 


265 


TABLE   OF  PIPE  SIZES 


(All  dimensions  in   indies.) 


NOMINAL  INSIDE 
DIAMETER 

ACTUAL  INSIDE 
DIAMETER 

ACTUAL  OUTSIDE 
DIAMETER 

THICKNESS 

NO.  OF  THREADS 
PER  INCH 

DIAMETER  OF 
DRILL 

.27 

.405 

.07 

27 

ft 

.36 

.504 

.08 

18 

1  : 

.49 

.675 

.09 

18 

:  -, 

-'••     "••••:  '    ;       '.       '    • 

.62 

.840 

.10 

14 

•  I 

,82 

1.050 

.11 

14 

1* 

1.04 

1.315 

.13 

HI 

Ut 

If 

1.38 

1.660 

.14 

HI 

if 

i* 

1.61 

1.900 

.14 

Hi 

if- 

2 
2* 

2.06 
2.46 

2.375 

2.875 

.15 
.20 

11* 

8 

1 

3 

3.06 

3.500 

.21 

8 

3* 

3.56 

4.000 

.22 

8 

3H 

4 

4.02 

4.500 

.23 

8 

4A 

...•4* 

4.50 

5.000 

.24 

.  8 

5 

5.04 

5.560 

.25 

8 

6 

6.06 

6.625 

.28 

8 

7 

7.02 

7.625 

.30 

8 

8 

7.98 

8.625 

.32 

8 

9 

9.00 

9.625 

.34 

8 

10 

10.01 

10.750 

.36 

8 

11 

11.00 

11.750 

37 

8 

12 

12.00 

12.750 

.37 

8 

13 

13.25 

14.000 

.37 

8 

14 

14.25 

15.000 

.37 

8 

15 

15.40 

16.000 

.28 

8 

16 

16.40 

17.000 

.30 

8 

17 

17.30 

18.000 

.34 

8 

.  ~ 

CHAPTEE  X 

INSTRUCTOR'S  GUIDE 
SUGGESTIONS  TO  TEACHERS 

It  is  the  aim  of  this  chapter  to  give  briefly  the  point-of-view 
of  the  authors  on  the  results  to  be  secured  in  this  course  together 
with  their  ideas  on  the  administration  of  the  course  and  the 
methods  of  securing  results. 

The  course  is  the  result  of  a  development  extending  over  a 
period. of  more  than  twenty  years,  during  which  time  the  prob- 
lem of  teaching  drawing  has  been  carefully  studied.  In  every 
case  the  method  herein  presented  has  been  repeatedly  tested  in 
the  classroom.  One  of  the  fundamental  ideas  on  which  this 
course  is  based  is  that  each  division  of  the  work  requiring  par- 
ticular knowledge  or  skill  must  be  given  concentrated  attention. 
Another  idea  of  equal  importance  is  that  in  drawing,  work 
should  be  progressive  from  the  standpoint  of  both  theory  and 
technique.  A  study  of  the  outline  given  herewith  will  show  how 
these  two  ideas  of  progression  and  concentration  have  been  woven 
into  the  fabric  of  the  course.  The  principles  and  methods  pre- 
sented in  each  division  have  been  carried  into  the  following 
division  in  such  a  way  as  to  relieve  the  suddenness  of  the  transi- 
tion made  and  to  give  opportunity  for  further  development. 

The  method  of  the  course,  viz.,  to  concentrate  upon  one 
element  in  drawing  in  each  division  of  the  course  and  to  make 
use  of  this  element  in  the  succeeding  divisions,  is  exemplified 
in  the  development  of  the  orthographic  theory  where  the  top 
and  front  views  only  are  given  in  the  first  presentation,  where 
the  front  and  side  views  are  given  in  the  second  presentation, 
and  later  where  three  views— front,  top,  and  side — are  given. 
On  the  side  of  technique  the  method  is  exemplified  in  Chapters 
I,  II,  III,  and  IV,  where  the  emphasis  falls  successively  on 

266 


INSTRUCTOR'S  GUIDE  267 

perspective  sketching,  orthographic  sketching,  pencil  mechan- 
ical drawing,  and  tracing.  It  should  be  noted,  also,  that  the 
element  in  each  division  is  continued  in  succeeding  divisions. 

Demonstrations.  It  is  the  belief  of  the  authors  that  instruc- 
tion on  the  manual  part  of  the  drawing  course  can  be  given 
most  effectively  by  means  of  demonstrations.  The  instructor 
should  present  to  the  class  the  proper  method  of  manipulating 
the  instruments  and  materials  by  actually  going  through  the 
process  himself,  calling  attention  to  important  points  and  ex- 
plaining each  step  as  he  proceeds.  The  principle  upon  which 
each  movement  or  process  is  based  should  be  given  in  order 
that  the  student  may  not  only  know  how  a  thing  is  done,  but 
also  why  it  is  done  in  one  way  rather  than  another.  For  exam- 
ple, it  is  not  sufficient  to  say  that  the  paper  should  be  fastened 
in  the  upper  left  hand  corner  of  the  drawing  board.  The  rea- 
sons for  so  placing  it  should  be  given.  First,  it  should  be 
explained  that  the  T-square  is  more  easily  manipulated  when 
lines  are  drawn  near  the  head.  Second,  that  with  the  sheet  in 
this  position  the  arm  may  rest  on  the  board  while  doing  lettering 
or  other  freehand  work  in  the  lower  part  of  the  sheet. 

The  demonstrations  may  be  given  to  the  class  as  a  whole 
or  to  groups  of  students  as  conditions  may  warrant.  In  gen- 
eral better  results  will  be  obtained  when  the  demonstration  is 
so  timed  that  the  student  may  make  use  of  the  information 
immediately. 

There  is  a  tendency  on  the  part  of  instructors  to  give  too 
much  material  in  one  demonstration  or  to  spend  too  much  time 
on  minute  details  which  the  student  with  his  limited  knowledge 
of  the  subject  cannot  appreciate  and  which  tend  to  obscure 
the  really  vital  points.  Demonstrations  should  not  occupy  more 
than  ten  or  fifteen  minutes.  The  material  should  be  selected 
with  a  view  to  its  immediate  usefulness,  leaving  many  minor 
details  for  individual  instruction  or  for  class  or  group  dem- 
onstration after  students  have  had  some  experience  in  carrying 
out  the  instructions  of  the  first  demonstration. 

The  following  outline  of  a  demonstration  on  the  use  of  the 
ruling  pen  is  given  as  an  example: 


268  MECHANICAL  DRAWING 

DEMONSTRATION  ON  THE  RULING  PEN 

I.  Use. 

A.  Billing  lines  in  ink. 

1.  Guided  by  T-square. 

2.  Guided  by  triangles. 

3.  Guided  by  irregular  curves. 

II.  Setting  and  Filling. 

A.  Set  the  pen  by  means  of  the  thumb  screw  to  the  approxi- 
mate width  of  the  line  desired. 

B.  Fill  the  pen  by  inserting  between  its  nibs  the  quill  which 
is  attached  to  the  stopper  of  the  ink  bottle.     There  should  be 
about  one-quarter  of  an  inch  of  ink  in  the  pen.     There  should  be 
no  ink  on  the  outside  of  the  nibs. 

C.  Adjust  the  pen   to  exact  width  of  line  by  drawing  trial 
lines  on  the  margin  of  the  sheet. 

III.  Manipulation. 

A.  Hold  the  pen  with  the  first  finger  just  above  the  thumb 
screw  and  with  the  second  finger  against  the  right  edges  of  both 
blades. 

B.  Place  the  pen  against  the  ruling  edge  with  its  axis  in  a 
vertical  plane.     The  pen  may  lean   slightly  in  the   direction  of 
motion. 

C.  The  forearm  should  be  at  right  angles  to  the  line  being 
drawn. 

D.  Draw   slowly  from   left  to  right  or   from   bottom  to   top. 
The  tips  of  the  third  and  fourth  fingers  should  slide  on  the  ruling 
edge. 

IV.  Cleaning. 

A.  Clean  the  pen  frequently  by  inserting  a  cloth  at  the  side 
and  by  drawing  it  out  between  the  nibs. 

B.  Open   the   pen    and   clean   it   thoroughly   before   laying  it 
away. 

The  following  points  which  are  not  essential  at  first  should 
be  left  for  a  later  demonstration : 

I.  Sharpening  the  pen. 
II.  Drawing  lines  tangent  to  arcs. 

III.  Drawing  irregular  curves. 

IV.  The  advantages  of  pens  of  different  designs  or  makes. 

Individual  Instruction.    As  stated  above,  the  instructor  can- 
not anticipate  all  of  the  needs  of  the  student  when  giving  a 


INSTRUCTOR'S  GUIDE  269 

demonstration  without  going  too  much  into  detail,  nor  can  he 
expect  that  every  point  made  in  the  demonstration  will  be  per- 
manently fixed  in  the  mind  of  the  student.  The  demonstration 
should  therefore  be  supplemented  by  individual  instruction. 
The  instructor  should  make  a  study  of  each  individual's  needs 
with  a  view  to  giving  just  the  instruction  required.  This  type 
of  instruction  must  be  carefully  given,  as  too  close  attention  to 
the  work  of  a  student  may  keep  him  from  developing  ability  to 
do  independent  work.  Under  proper  instruction  the  student 
will  develop  the  power  to  take  the  data  given  him  and  with  it 
reach  the  proper  solution.  The  student's  power  to  reason  for 
himself  can  be  developed  by  answering  his  questions  with  counter- 
questions  and  offering  suggestions  designed  to  lead  him  to  think 
for  himself.  He  should  not  be  told  to  do  a  thing  in  a  certain 
way  without  being  given  a  reason  for  so  doing  it,  unless  it  is 
a  matter  of  arbitrary  convention. 

Recitations.  In  addition  to  the  material  which  is  given  in 
the  demonstration  there  is  a  considerable  amount  of  informa- 
tion which  may  best  be  secured  by  a  study  of  the  text.  An 
attempt  on  the  part  of  the  instructor  to  give  all  information 
verbally  will  lead  his  students  to  rely  on  him  entirely  and  will 
take  away  the  incentive  for  them  to  get  needed  information 
themselves. 

The  recitation  is  invaluable  to  test  the  student's  knowledge 
of  the  principles  and  methods  given  in  the  text.  It  may  also 
be  used  to  advantage  as  a  review  of  the  demonstration  and  to 
ascertain  the  effectiveness  of  the  instruction  given  by  that 
method. 

The  recitation  may  be  carried  on  by  means  of  questions 
such  as  those  given  at  the  close  of  Chapters  I,  II,  III,  and  IV. 
In  answering  some  questions  the  student  may  be  required  to 
draw  a  sketch  on  the  blackboard  and  explain  it. 

Quizzes.  After  the  completion  of  each  general  division  of 
the  course,  the  student's  knowledge  of  the  subject  matter  in 
that  division  should  be  tested  by  requiring  him  to  answer  sev- 
eral questions  or  to  make  a  drawing  which  will  test  his  knowl- 
edge of  the  fundamentals.  Questions  should  be  answered,  as 
far  as  possible,  by  means  of  sketches.  Every  opportunity  should 


270  MECHANICAL  DRAWING 

be  taken  to  have  the  student  use  drawing  as  a  means  of  expres- 
sion. Questions  similar  to  those  at  the  close  of  Chapters  I, 
II,  III,  and  IV  may  be  used  for  the  quizzes. 

Problems.  As  previously  stated,  an  attempt  has  been  made 
to  make  the  course  progressive  both  in  theory  and  technique. 
The  problems  of  the  course  were  selected  and  arranged  with  this 
in  view.  Except  in  the  chapter  on  Perspective  Sketching  the 
problem  for  each  plate  may  be  selected  from  a  group  of  prob- 
lems. The  group  system  makes  it  possible  to  adapt  the  problem 
to  the  ability  of  the  student.  The  system  also  reduces  the 
tendency  for  one  student  to  copy  from  another.  In  all  but  a 
few  problems  the  student  finds  it  necessary  to  work  out  his  own 
solution.  As  a  rule  he  is  required  to  read  the  given  drawing 
and  to  understand  the  form  of  the  object  represented  before 
he  can  proceed  with  his  drawing.  In  many  cases  the  choice  of 
views  is  left  entirely  to  the  student.  The  dimensioning  also 
presents  a  problem  which  the  student  must  solve  by  using  the 
general  principles  given  him  and  from  his  knowledge  of  shop 
methods.  "Where  this  knowledge  is  limited  the  instructor  must 
supply  the  necessary  information. 

What  has  been  called  a  type  problem  is  given  with  each 
student  problem.  The  type  problem  serves  to  guide  the  student 
in  the  solution  of  his  problem.  The  type  problem  shows  a  typical 
or  standard  arrangement  of  views,  dimensions,  etc.,  and  a  tech- 
nique which  serves  as  an  ideal  toward  which  the  student  should 
strive. 

Perspective  Sketching  affords  the  most  natural  method  of 
representing  objects  in  outline.  It  gives  a  valuable  training  in 
coordinating  the  hand  and  eye  in  drawing  freehand  lines  and 
estimating  proportions.  It  serves  as  an  intermediate  step  be- 
tween observing  an  object  and  drawing  its  orthographic  views. 
The  student  who  first  draws  a  perspective  sketch  of  an  object 
becomes  so  familiar  with  every  detail  of  it  that  he  cannot  fail 
to  have  a  clearer  mental  image  of  its  form  when  he  attempts 
to  draw  its  orthographic  views.  By  its  use  he  learns  the  more 
readily  to  interpret  the  orthographic  drawing.  These  considera- 
tions together  with  a  growing  use  of  this  type  of  representation 
in  drafting  practice  justifies  its  place  in  a  drafting  course. 


INSTRUCTOR'S  GUIDE  271 

The  theory  on  which  Perspective  Sketching  in  this  course  is 
based  is  limited  to  a  very  simple  treatment  of  45°  perspective. 
This  treatment  was  adopted  to  make  this  division  of  the  work 
in  keeping  with  the  elementary  nature  of  the  whole  course  and 
with  the  idea  that  the  perspective  sketching  should  occupy  but 
a  small  fraction  of  the  total  time  given  to  the  course.  The  time 
allotted  to  this  division  of  the  work  should  be  about  one-fifth 
of  the  total  time  given  to  the  work  of  the  first  four  chapters. 
An  extension  of  theory  given  at  the  end  of  Chapter  I  may  be 
used  to  broaden  the  course  if  desired.  . 

It  is  desirable  that  all  members  of  a  class  be  kept  reasonably 
near  together  in  each  division  of  the  course.  To  make  this 
possible  extra  problems  are  given  which  may  be  assigned  to 
those  who  forge  ahead. 

Orthographic  Sketching.  The  work  of  this  chapter  offers 
opportunity  for  improvement  in  freehand  technique  and  a  con- 
siderable amount  of  drill  in  the  fundamental  principles  of 
orthographic  representation.  The  treatment  of  orthographic 
theory  is  made  simple.  It  is  applicable  to  the  requirements  of 
drafting  room  practice.  It  is  essential  to  the  success  of  the 
plan  given  that  the  student  should  consider  the  object  to  be 
placed  in  a  fixed  position.  To'  obtain  each  of  the  required  views 
he  must  imagine  himself  placed  in  the  correct  position  with 
respect  to  the  object.  The  practice  of  shifting  the  position  of 
the  object  usually  results  in  a  confusion  of  the  principles  which 
relate  to  the  position  of  views  with  reference  to  each  other. 

Another  point  of  considerable  importance  is  that  problems 
are  simple  and  numerous.  A  large  number  of  problems  gives 
drill  in  orthographic  representation,  and  acquaints  the  student 
with  a  variety  of  forms  and  arrangements  of  views. 

Technique.  The  authors  believe  that  securing  good  tech- 
nique, both  freehand '  and  mechanical,  is  as  educative  as  an 
acquisition  of  a  knowledge  of  the  theory  of  drawing.  The 
highest  type  of  technique  is  not  easy  to  obtain  under  any  con- 
ditions. Proper  instruction  and  classroom  administration  are 
necessary  to  secure  good  results. 

A  first  requisite  is  to  establish  a  satisfactory  standard.  This 
standard  must  be  high  and  yet  not  unattainable.  Often  good 


272  MECHANICAL  DRAWING 

drawings  from  a  previous  term's  work  may  be  exhibited  and 
will  prove  to  be  of  great  value  in  showing  the  student  what  has 
been  accomplished  by  other  students  who  have  worked  under 
similar  conditions.  Individual  instruction,  in  which  the  instruc- 
tor draws  a  few  sample  lines,  explains  the  proper  sharpening  .of 
the  pencil  or  the  setting  of  the  pen  and  its  correct  manipula- 
tionf  cannot  be  overestimated  as  a  means  of  establishing  a  good 
standard  of  technique. 

The  beginner  usually  does  not  possess  the  necessary  skill  to 
make  the  minute  detail  of  a  drawing  perfect.  Neither  has  he 
an  appreciation  of  the  relation  of  these  details  to  the  general 
effect  of  the  drawing.  For  example,  he  is  not  likely  to  notice 
slight  imperfections,  such  as  running  by  a  corner  or  making 
the  two  barbs  of  an  arrowhead  non-symmetrical  with  respect 
to  the  dimension  line.  However,  it  is  such  imperfections  which, 
taken  in  the  aggregate,  affect  the  general  appearance  of  a  draw- 
ing. Details  of  this  kind  must  be  given  constant  attention  by 
the  instructor.  In  most  cases  calling  the  student's  attention 
to  the  defects  in  the  drawing  does  not  make  a  sufficient  impres- 
sion. He  should  be  required  to  correct  the  defects  by  erasing 
and  redrawing  the  lines. 

Lettering.  As  a  rule  it  is  at  first  more  difficult  to  obtain  a 
satisfactory  freehand  technique  than  a  satisfactory  mechanical 
technique.  To  offset  this  tendency  a  number  of  plates  of  letter- 
ing have  been  designed.  They  are  so  arranged  that  if  each  fol- 
lows the  drawing  plate  of  the  same  number,  considerable 
practice  will  be  had  before  it  becomes  necessary  to  do  lettering 
on  the  regular  drawing  plates.  Here  again  the  ideas  of  progres- 
sion and  concentration  are  prominent  features.  The  letters  of 
the  alphabet  are  grouped  according  to  characteristics  of  form, 
and  are  arranged  in  the  order  of  the  difficulty  with  which  they 
are  drawn.  Only  four  or  five  new  letters  are  given  on  each 
plate.  Each  letter  is  practiced  individually  and  then  in  cgmr 
bination  with  those  of  previous  plates.  ;•;•;'.( 

In  the  early  stages  in  lettering  the  best  results  are  obtained 
when  the  work  is  done  in  short  periods  of  fifteen  or  twenty 
minutes  each  and  following  a  demonstration.  The  instructor 
should  draw  each  new  letter  on  the  board  to  large  scale,  and 


INSTRUCTOR'S  GUIDE  273 

call  attention  to  the  number,  order,  and  direction  of  strokes, 
and  to  important  points  in  the  form  and  proportion  of  each 
letter.  He  should  give  suggestions  concerning  the  making  of 
strokes,  the  spacing  of  letters,  etc. 

The  outline  for  a  sample  demonstration  follows : 

PLATE  6 

I.  The  Capital  Letter  F. 

1.  First  stroke  vertical. 

2.  Second  stroke  horizontal  on  the  upper  guide  line.     Make 
slightly  less  in  length   than  the  width  of  the  H,  which  is  the 
standard  of  width. 

3.  Third  stroke  horizontal.     Make  it  slightly  above  the  middle 
of  the  space,  on  the  same  level  with  the  horizontal  stroke  of  the 
H.     Make  its  length  slightly  more  than  half  the  length  of  the 
second   stroke. 

II.  The  Capital  Letter  E. 

1.  First  stroke  vertical. 

2.  Second  stroke  horizontal  on  the  lower  guide  line.     Make  it 
equal  in  length  to  the  width  of  the  H. 

3.  Third    and    fourth    strokes    exactly    like    similar    strokes 
of  the  F. 

III.  The  Capital  Letter  N. 

1.  First  stroke  vertical. 

2.  Second  stroke  vertical.     Space  it  a  distance  from  the  first 
stroke   equal   to   the   width   of   the   H.      This   distance   must  be 
estimated  by  judging  the  horizontal  distance  from  the  first  stroke 
to  the  beginning  of  the  second  stroke. 

3.  Third  stroke.     This  is  an  inclined  stroke   drawn   between 
two  fixed   points.     The  beginner  should  move  the  pencil  in  the 
direction  of  the  stroke,  to  get  a  sense  of  its  direction,  before 
drawing  the  stroke. 

IV.  The  Capital  Letter  M. 

1.  First  stroke  vertical. 

2.  Second  stroke  inclined.     The  angle  at  which  this  stroke  is 
drawn  determines  the  width  of  the  letter.     It  must  therefore  be 
carefully  estimated.    The  width  of  the  letter  is  equal  to  its  height. 
The  stroke  ends  about  one-fifth  of  the  height  of  the  letter  above 
the  lower  guide  line. 

3.  The  third  stroke  makes  the  same  angle  to  the  vertical  as 
does,  the   second  stroke.     The   starting  point  must   be  carefully 
located  to   get  this  angle   correct  and  to  make  the  end  of  the 
second  stroke  fall  half  way  between  the  two  vertical  stems. 

4.  Fourth  stroke  vertical. 


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INDEX 


Accuracy,  87 

Accuracy  cf  measurements,  235 

Acme  threads,  159 

Addendum,  168 

Adjacent  parts,  crosshatching  of,  246 

Adjustable  square,  234 

Angle  of  inclination,  15 

Angles 

constructing  in  multiples  of  5°   and 
10°,  226 

dimensioning,  64 
Architect's  scale,  137 
Arrangement    of   dimensions   in    ortho- 
graphic sketch,  57 
Arrangement  of  views  on  sheet,  244 
Arrowheads,  184 
Assembly  drawing 

purpose  of,  252 

details  from,  246 
Auxiliary  views,  255 
Axes,  derivation  of,  Isometric,  257 


Balancing  a  title,  89 

Bevel  gears,  169 

Bill  of  material,  14* 

Blueprint  paper,  127 

Blueprinting,  117 

Board,  drawing,  130 

Bolt,  tap,  163 

Bolts  and  nuts,  161 

Border  line,  111,  112 

Border  rectangle,  20,  86 

Bow  compass,  drawing  circle  with,  86 

Bow  dividers,  141 

Bow  pen,  111,  141 

Bow  pencil,  141 

Breaks,  conventional,  154 


Cabinet  drawing,  260 
Calipers,  235 
Cap  screw,  163 
Center  lines 

circular,  69 

principal,  69 

radical,  69 

secondary,  69 

Checking  measurements,  241 
Circle 

drawing  with  bow  compass,  86 

sketching,  71 


Circles 

concentric,  in  perspective,  36 

dimensions  of,  69 

Isometric,  259 
Circular  edges,  66 
Circular  pitch,  167 
Cloth,  tracing,  109,  127 
Compass,  111,  138 

Composition  in  lettering,  198,  201,  217. 
Concentric  circles  in  perspective,  36 
Constructive  stage 

in  perspective,  20 

of  orthographic  sketch,  56 

of  mechanical  drawing,  88 
Coordinate  paper,  231 
Coordinates,    locating    points    with,    in 

Isometric,  257 

Conventional  crosshatching,  153 
Corners,  representation  of,  53 
Crosshatching 

adjacent  parts,  246 

conventional,  69,  153 
Crosshatch  lines,  112 
Cube 

in  perspective,  15 

measure,  definition  of,  27 

measure  in  new  positions,  41 
Curve,  French  or  irregular,  136,  225 
Curved  strokes  in  lettering,  184,  185 
Cylinder 

measure,  horizontal,  38 

measure,  in  new  positions,  41 

measure,  vertical,  33 
Cylindrical  surfaces 

dimensions  of,  69 

representation  of,  64 

Dedendum,  168 
Demonstration 

place  of,  267 

time   of,   267 

illustration,   268 

Details,  drawing  from  assembly,  246 
Diameter 

measuring  inside,  238 

measuring  outside,  238 
Diametral  pitch,  167 
Dimension 

figure,  89 

form,  57,  184 

line,  88,  111 


279 


280 


INDEX 


Dimensions 

arrangement     of    in     orthographic 

sketch,  57 

selection  and  arrangement,   232 
Dimensioning 

general  principles  of,  146 
cylindrical  surfaces  and  circles,  69 
radius,  95 
Distance 

measuring  center  to  center  of  holes 

239 

measuring  linear,  236 
Dividers,    140 
Dotted  lines,  88 
Drawing 

an  ellipse,  34 
board,  130 
Cabinet,  260 
from  the  object,  230 
Isometric,  256 
paper,  126 

steps  in  making,  231,  241 
Drawing  instruments 
bow  dividers,  141 
bow  pen,  141 
bow  pencil,  141 
compass,  138 
dividers,  140 
ruling  pen,  141 

Edges 

circular,    representation   of,   66 

inclined,  59 

invisible,  53 

straight,  52 

Ellipse,  to  draw  and  test,  34 
Enclosing  rectangle,  86 
Enclosing  solid  in  perspective,  21 
Engineer's  scale,  137 
Eraser,  129 
Erasing  shield,    130 
Erasure,   112 
Extension  lines,  88.  112 

Fastening  paper  to  board,  17,  83 
Figures 

and  notes,  147 

dimension,  89 

Filling  lettering  pen,  178,  198 
Finish,  methods  of  indicating.  166 
Finishing  stage 

for  mechanical  drawing,  88 

for  orthographic  sketch,  56 

in  perspective,  21 
Folding  rule,  233 
Foot   marks,    183 
Foreshortening,  definition  of.   H 


Fraction  and  whole  number.  186 
French  curve,  136,  225 

Gears, 

bevel,  169 

spur,  167 

worm,  169 
General  drawing,  252 

Heads,  arrow,  184 
Heights  of  letters,  183 
Horizon,  definition,   13 
Horizontal  lines,  ruling,  85 

Inch  marks,   183 
Inclination,  angle  of,  15 
Inclined  edges,  59 
Inclined  lines,  93 
Inclined   surfaces,   59 
Ink,  black,  109 
Inking, 

order  of,  112 

lines,  order  of,  229 
Inside  diameter,  measuring  of,  238 
Instruction,  individual,  268 
Instruments 

drawing,   138 

measuring,  233 
Invisible  edges,  53 
Invisible  lines,  88 
Irregular  curve,  136,  225 
Isometric  drawing,  256 

derivation  of  axes,  257 

Isometric  circles,  259 

Isometric  lines,  257 

locating    points    with    three    coordi- 
nates, 258 

locating  points  with  two  coordinates 
257 

non-Isometric  lines,  257 

Lead,  165 
Lettering 

composition,  198,  201,  217 

curved   strokes,    184,    185,    211.    215 
216 

horizontal  strokes,  189 

inclined,  lower  case,  207 

inclined  stroke,  189 

in  ink,  177,  197 

in  pencil,  177 

instruction  for.  184 

pencil,  182 

plate,  181 

position  of  hand  in,  178 

preparation  of  tracing  cloth.   107 

strokes,  drawing  the,  183 

time  given  to,  272 


INDEX 


281 


Letters 

form  and  proportion  of,  176 

inclined,  lower  case,  slope  of,  20" 

spacing  curved  strokes,  193 

spacing  of,  176,  189,  211 

spacing  of,   176 

strokes  for,   176 
Levels, 

scale  of,  cylindrical  objects,  34 

scale  of,  rectangular  objects,  24 
Line 

border,   112 

dotted,  88 

invisible,  88 

object,  111 

table,  27 

notation,  145,  111 
Linear  distance,  measuring,  236 
Line,  center 

circular,  69 

principal,  69 

radical,  69 

secondary,  69 
Lines 

Crosshatch,  112 

extension  and  dimension,  88,  112 

inclined,  93 

in  perspective,  direction  of.  114 

Isometric,  257 

non-Isometric,  257 

object,  111 

shade,  173 

Machine  screws,  163 
Marks,  foot  and  inch,  183 
Material,  bill  of,  148 
Measure 

cube,  definition,  27 

cube  in  new  positions,  41 

cylinder  in  new  positions,  41 

cylinder,  vertical,  33 
Measurements 

accuracy  of,  235 

center  to  center  of  holes,  239 

checking,  241 

in  foreshortening,  14 

in  perspective,  14,  25,  27 

linear  distances,  236 

radii,   240 

taking  of,  235 
Measuring  instruments,  233 
Multiple  thread,  163 

Notation  of  lines,  145 
Notes,  89,  147,  201 
Number  and  fraction,  186 
Nuts  and  bolts,  161 


Object 

lines,   111 

sketching  from,  230 
Orthographic 

sketching,  50,  271 

views,  definition,  50 

front  and  side,  58 

top  and  front,  50 
Outside  diameter,  measuring  of,  238 

Paper 

blueprint,  127 

coordinate,   231 

drawing,  126 

to  fasten  to  the  board,  17,  8." 

tracing,  127 

Van  Dyke,  128 
Partial  view,  256 
Pen 

bow,   111,  141 

care  of,  178 

filling,  178,  198 

ruling,   109,   141 
Pencil 

lettering,  182 

to  sharpen,  18 
Pencils 

requisites  of,  128 

manipulation,  129 
Perspective 

concentric  circles  in,  36 

direction  of  lines  in,  14 

measure  cube  in  new  positions,  41 

measure  cylinder  in  new  positions,  42 

measurements  in,  14,  25,  27 

sketch,  definition  of,  13 

the  cube  in,  15 

the  measure  cube  in,  27 

the  table  line,  27 

to  center  sketch  on  sheet,  30 
Perspective  sketching 

constructive  stage  in,   20 

enclosing  solid  in,  27 

finishing  stage  in,   21 

use  of  orthographic  drawing,  54 

value  of,  270 
Pipe  threads.  159 
Pitch 

of  thread,  154,   165 

circular,  167 

diametral,  167 

Plane  surfaces,  representation  of.  52 
Plate 

lettering  instructions  for,  184 

lettering  of,  181 
Problem,  type,  54,  270 


282 


INDEX 


Problems 

extra,  271 

three  view,  77 

Proportional  inch  scale,  138 
Protractor,   144 

Quarter  section,  68 
Quiz,  260 

Radii,  measuring,  240 
Radius  dimensions,  95 
"Reading"  a  drawing,  50 
Recitation,    269 
Rectangle 

border,  20,  80 

enclosing,  86 
Rivet,  proportions,  173 
Rule,  folding,  233 
Ruling  horizontal  lines,  85 
Ruling  pen 

adjustment  of,   142 

care  of.  143 

filling,  142 

manipulation  of,  109,  142 

requisites  of,  141 

sharpening,  143 
Ruling  vertical  lines,  85 

Scale 

of  the  drawing,  93 

of  heights,  183 

of  levels,  cylindrical,  34 

of  levels,  rectangular,  24 

of  widths,  183 

steel,  234 
Scales 

architect's,    137 

engineer's,  137 

proportional  inch,  138 
Screw 

cap,  163 

machine,  163 

set,  163 
Screw  threads 

acme,  159 

pipe,  159 

square,  158 

U.  S.  Standard,  158 

V-Thread,  154 
Sectional  views 

breaks,  154 

broken   line,    150 

half  section,  149 

partial,  150 

quarter  section.  68.  150 


revolved  section,  151 

section  through  ribs,  shafts,  bolts,  152 

separate  section,  152 
Section  lining,  69 
Selecting  views,  231 
Set  screws,  163 
Shade  lines,  173 
Sharpening  pencil,  18 
Shield,  erasing,  130 
Sketch,  perspective 

constructive   stage,    20 

finishing  stage,  21 

perspective,  definition  of,  13 

to  center  on  sheet,   30 
Sketching 

a  circle,  71 

from  the  object,  230 

orthographic,  50,  271 

perspective,  value  of,  270 

position  of  hand  and  pencil,  19 
Spacing 

curved  stroke  letters,  193 

of  letters,  176,  189,  211 

of  words,  176,  189,  198 
Springs,  161 
Spur  gears,  167 
Square 

adjustable,  234 

T-131 

threads,  158 
Stage 

constructive    for    mechanical    draw- 
ing, 88 

construction    of    perspective    sketch, 
20 

construction  of  orthographic  sketch, 
56 

finishing  for  mechanical  drawing,  88 

finishing  of  orthographic  sketch,  56 

finishing  of  perspective  sketch,  21 

finishing  for  mechanical  drawing,  88 
Steel 

scale,  234 

tape,  234 

Straight  edges,  52 
Strokes,  drawing  the,   183 

curved.  184,  185,  211,  215,  216 

horizontal  in  lettering,   189 

inclined  in  lettering,  189 

vertical  in  lettering,   189 
Strokes 

in  lettering,  173 

in  lettering,  order,  number,  and  direc- 
tion of,  182 
Structural  details 

drawing  of,  170 

of  dimensioning.  172 


INDEX 


283 


rivet  proportions,  173 

structural  shapes,  171 
Stud,   163 
Stud  bolt,  163 
Sub-title,    244 
Surfaces 

cylindrical,  representation  of,  64 

inclined,  59 

plane,  representation  of,  52 

Table  line,  27 
Tacks,  thumb,  128 
Tangencies 

construction  of,  95,  117 

locating  points  of,  121 
Tap  bolt,  163 
Tape,  steel,  234 
Technique,  value  of,  271 
Thread 

multiple,  163 

pipe,  159 

screw,  154,  158,  159,  161,  163 

(See  Screw  Threads) 
Three  view  problems,  77 
Thumb  tacks,  128 
Title,  block,  S9 
Title,  sub,  244 
Titles 

balance,  89,  17l> 

commercial,   148 

contents  of,  89,  147,  179 

design  of,  179 

spacing  of  lines,  179 

steps  in  design,  179 


style  of  letters,  179 

trial  sheet,  89 
Tracing 

cloth,  109,  127 

paper,  127 

trimming  the,  112 
Triangles 

use  of,  133 

combination  of,  136 

direction  of  drawing  lines,  135 

testing,  133 

.'{0°   to  60°,  133 

45°,    133 
T-square,  131 
Type  problem,  54,  270 

I".  S.  Standard  thread,  158 

Van  Dyke  paper,  128 
Varnishing  paints,  definition  of,  14 
Vertical  lines,   ruling,  85 
Views 

arrangement  on  sheet,  244 

auxiliary,  255 

definition  of,  50 

partial,  256 

relation  of  front  and  side,  58 

relation  of  top  and  front,  50 

sectional,  149,  150.  351,  152 

selecting  of,  231 

Widths  of  letters,  182 
Words,  spacing,  176,  189,  198 
Worm  gears,  169 


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UNIVERSITY  OF  CALIFORNIA  LIBRARY 


